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Backlinks in SEO: what are they?

A backlink, also called an inbound link or incoming link, is a hyperlink on a web page that points to another page, usually on a different site. In organic search (SEO), backlinks matter because they act as recommendations or votes of confidence from one site to another, telling search engines that the linked content is relevant and worth attention.

diagram of computers connected by links - SEO backlinks

Search engines such as Google use backlinks to:

  • Assess a site’s popularity and credibility: a site that receives many quality backlinks is seen as more trustworthy and relevant.
  • Improve rankings in search results: backlinks directly affect where a site sits in the search engine results pages (SERP).
  • Help crawlers explore the web: search-engine bots follow backlinks to discover new pages to index.

Backlink campaigns usually sit inside an SEO strategy, on the off-site side: a link-building strategy. The SEO consultant no longer waits for backlinks that appear “naturally” from sources they do not control. They try to generate more of them, or better ones. The backlink then gets more complex in theory: it can carry attributes (nofollow, for example) and even a quality judgment from Google. That classification of a backlink as good or bad depends on many criteria, often tied to the context of the link, which SEO specialists try to influence.

How can a backlink affect a site’s ranking in the Google SERP? And how do you run a link-building strategy to earn good backlinks?

In HTML, a backlink is represented by the link tag, which contains the target URL: the address of the content you want to point to. That tag opens and closes around one or more keywords, which make up the anchor text. That is the phrase a visitor can click to reach the linked content.

  • link anchor *

For Google to start judging the quality of a backlink, the anchor text has to be relevant to the target content: it should define that content, or at least invite a click, in an appropriate thematic and semantic context. An anchor such as “General de Gaulle” pointing to Napoleon’s Wikipedia page is unlikely to look relevant. These anchors are much closer:

Of all European emperors, Napoleon I is probably one of the best known.

If you want to learn more about Napoleon and his conquests, click here.

Napoleon’s Wikipedia page will teach you a lot more about his history: https://fr.wikipedia.org/wiki/Napoléon 1er

Then, for a backlink to be a good one, the anchor has to relate to the target page, and the page that sends the link has to cover a close or identical topic. If the link to Napoleon’s Wikipedia page sits in an article that only describes General de Gaulle’s life, Google is unlikely to treat it as high quality. If it sits in an article on major French military figures, and that piece gives Napoleon as much space as General de Gaulle (paragraphs of similar length, clear subheadings…), the link starts to look coherent to Google in that context.

If you have a site, a blog, or even a mailbox, you already know spam: an unwanted message that shows up in an email or a comment and, most of the time, asks you to click a link. Spam techniques appeared both to send visitors to a specific page and to collect something, such as personal data. “Spammy” content or comments on blogs and forums exist first to help their author, not the page they are posted on. Spammy comments often contain links to dubious sites so those sites can borrow the host site’s SEO popularity, or “link juice” (see below).

To stop popularity leaking through links you do not control, you can add an attribute to backlinks: rel=“nofollow”. That is an instruction to search engines when they find the link on the page: the sending site does not “stand behind” the link, so they should not pass popularity. A blog can therefore apply a default “nofollow” attribute to every link visitors publish in comments, and protect its rankings by protecting its popularity.

  • link anchor *

Logically, for a backlink to help a site’s rankings, it should not carry the “nofollow” attribute, or it will be treated as openly disavowed. Backlink quality is also a question of legitimacy.

What can also change a backlink’s quality is its position inside the source page. Google treats a link in context as more relevant than a link sitting alone, disconnected from a semantic environment. For SEO performance, it is more effective to place a backlink inside a paragraph of text than, for example, in a menu.

A common, and more or less outdated, practice is to place backlinks in a site’s footer. The backlink then appears on every page and passes any popularity those pages have to the target site. Google is not fooled: a position below every other element on the page, usually in a smaller font, signals that the link is not really meant to be clicked. Google then flags the backlink as openly “SEO” and gives it less weight when it calculates popularity.

To limit abuse, when the same link appears several times on a page, Google only counts the first one for relevance and popularity. Only the first anchor contextualizes the link, and only the position of that first link on the page matters.

So backlink quality is a mix of criteria, plus a strategic position on the page: the more contextualized it is, and the higher it sits in the text, the more likely Google’s algorithm is to treat it as a quality backlink.

drawing of an SEO consultant at a desk running a backlink campaign

Popularity at the center of Google’s algorithm

After defining what a good backlink looks like, it is worth a few lines on how Google’s algorithm ranks results for a given query.

Google wants to give the visitor the most relevant answer to their question. To do that, it has to find the content that, in form and substance, is most likely to satisfy them. It then walks its index for the strongest matching results. To build that index, the bots crawled a large number of sites and indexed their content: length, structure, semantics. They also ran those pages through the Panda and Penguin filters. At that stage, some results already stand out and match the intent of the query. They still have to be ordered. How does Google decide what to show first? To rank them, it looks at the most popular content, the content other users on the web already like. Backlinks are clearly a signal of that popularity.

A site that covers a topic in depth with rich content already gets Google’s attention. If that site also receives many backlinks from other quality sites in a close topic, it has a strong chance of making the short list and landing on SERP #1. Content and link building are two of the pillars of SEO (the third is technical SEO).

Link juice

Every link-building strategy that aims at good backlinks rests on one star concept: link juice. The idea applies to both internal and external links.

The image describes the transfer and dilution of popularity that happens when a link is placed from one page to another. People also talk about a transfer of “PageRank”, as a measure of a page’s popularity.

To keep the fruit-juice metaphor, picture a 1L bottle filled to the brim. If you pour the juice into a single container, that container receives 1L. If you pour it into 2 containers, each receives only 50cl, split evenly. If you pour it into 3 containers, each receives only 1/3 of the bottle, or 33.3cl, and so on.

The same rule applies to a page’s PageRank. Take the homepage: if it offers 5 internal links in a main menu and 3 external links (backlinks) to other reference or partner sites, its PageRank (its popularity) is then transferred and divided by 8. Each linked page, internal or external, receives 12.5% of the homepage’s popularity.

From that simple rule, the more links a page receives, internal or backlinks, the more its popularity grows, because each source page has transferred a share of its own popularity. The core of an SEO link-building strategy is therefore to collect as much popularity as possible for your pages by earning as many quality backlinks as possible.

a drawing of a shopping cart in a backlink universe

An optimized link profile

A “link profile” describes a site’s off-site characteristics: the number of backlinks and of referring domains, how that set changes over time (gains or losses), the geographic spread of the source sites’ TLDs, the various anchors used and their share… Those are the indicators the SEO tool Ahrefs reports, among others. You can also judge the quality of a link profile and the popularity it is likely to bring the site.

Following the theoretical rules so far, how Google’s algorithm works, and its relevance and quality criteria, you can imagine the ideal link profile, the one that would bring a site the most popularity:

  • A large number of backlinks from quality sites. Those are sites with rich, documented content, focused on a precise topic, that themselves receive many backlinks

  • Links placed on pages whose topic is very close to the target page

  • Anchors optimized on strategic keywords for the content’s rankings

Here is the catch: Google is not fooled. A link profile that looks too perfect can raise a flag. The engine wants to stay in control and tries to stop anyone from manipulating its results. It assumes that backlinks generated naturally on the web, following a “I like this, so I recommend it” logic, are never perfectly optimized. They sometimes appear in comments, and therefore possibly as nofollow. They are sometimes placed on the raw URL rather than a keyword. They sometimes come from Canada, Belgium, or Switzerland.

To look credible to Google you therefore need to keep a share of lower-quality links, or even go out and acquire some when you judge the profile is too optimized. A link-building strategy is first a question of diversity.

To keep diversity in a link profile, you have to multiply acquisition methods, link types, and anchor types. Keep in mind that Google penalizes any attempt that looks too obvious, so publication of the links, whatever they are, also has to be spread over time and over a real period. A spike of new links could trip an alarm at Google and undo the work you put into popularity and SERP rankings (which, remember, is the point).

Create links from directories

Prefer topical directories that match your activity. If none exist, pick well-known general directories. Do your homework: the web moves fast, and directories appear and disappear almost as quickly as Google changes its algorithm. Each year has its flagship directory, the way Omniz or Yelp once were. Prefer a directory that will last, so you keep the benefit of the link for several years. Create a listing for your activity or your site: it includes a “Link” field where you can enter your site’s URL, often the homepage.

Create links from forums

On the same principle as directories, start with topical forums on authority sites in your field. If you cannot find any, use general forums with relevant threads. Become a contributor, ideally a regular one, and try to place your link in a comment, in the middle of appropriate text. It can then point to a page other than the homepage. Be careful: to reduce the chance that your comment is moderated and never published, the link has to add real value to the discussion, an information or a piece of an answer.

Publish comments on blogs

Pick reference blogs in your topic and write constructive comments on the pieces you agree with, or on the ones you want to challenge. Do not just drop your link. Add a real opinion or a piece of useful information: a testimony, an experience. Your link should preferably read as a complementary source to continue the debate or go deeper on the topic.

Get links from supplier and partner sites

The SEO value of “Partners” pages has been dismissed for years, because Google has learned to devalue pages that are only a list of links. That said, those pages still exist because the sites that host them treat them as a showcase: displaying suppliers, customers, and partners is a way to look credible and serious to visitors. So try to get links from the partner pages or modules of other companies you work with. The simplest path is still to ask.

Publish guest posts

If your expertise and your contributions have value in your market, approach serious blogs or sites on your topic and offer a guest article. You provide the content (it has to be well written and documented) with no other ask than a mention of your name and a link to your site. The host site wins because the publication helps them: traffic on the page, a stronger semantic field, organic keywords to rank on. On your side, you should have earned a quality backlink.

Use social networks

Run contests or sharing incentives on your brand’s social networks to generate a large number of backlinks and traffic to your site. Even if backlinks from social networks do not carry the same SEO weight, they still send Google signals of your notoriety and of your popularity with your audience.

Pay for the writing and publication of sponsored articles

This practice means selecting topical sites and blogs related to your activity and contacting the writer or blogger to propose a subject that will include a link to your site. Most of the time the blogger writes from a brief you send, so the publication stays on their editorial line. In exchange, you pay a fee. Google’s policy is to penalize paid links when it detects them, so some sites prefer to be explicit and put a clear “Sponsored article” mention above your piece, which then puts the publication in the advertising field and relaxes Google’s tolerance.

Commission online press articles

In the same way you can commission a sponsored article, you can commission a press article about you. A web media outlet usually has much more popularity with users and with Google. Its content more often reaches the first page of results, especially on a company name, a brand, or a person. For the outlet, having a journalist write a piece, sometimes as an interview or an op-ed, is expensive. The journalist has to stay on the editorial line and make sure the topic will interest the audience. You can try to generate a piece for free by sending press releases, hoping the topic catches the outlet’s attention and they decide to “invest” in an article. You then have no guarantee that the article will frame the information the way you want, or even place a backlink to your site. Or you can raise your odds and pay for the published article.

Know that the price is often much higher than a classic sponsored article, because you are paying for the writer’s time and editorial skill as much as for the placement of a contextualized link and the ranking potential of the content. A backlink from an online press site is a strong source of popularity. It is a path worth considering.

Build a PBN

The last method, and not a small one, is to create a network of satellite sites called a PBN (Private Blog Network), filled with topical content and meant to link to your site on a regular basis. For a PBN to work and deliver its full SEO popularity, it has to be designed carefully so Google’s bots do not detect it. That means no links between the PBN sites, broader semantic fields, and a residual popularity on those sites by choosing expired domain names that already have a decent number of backlinks.

Want to know more about these complex but effective link-building methods? Our SEO agency can talk through your SEO problems and support the work.

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