Simply put, a backlink is a link from one website to another.

In other words, if Site A links to Site B then it can be said that Site B has received a backlink from Site A.

Sites receive backlinks usually because they have something in common with the linking sites. If Site A is a blog about philosophy and Site B is Wikipedia, for example, then it wouldn’t be surprising to see a blog post on Site A linking to a page about Plato, Nietzsche or Satre on Site B.

A backlink should not be confused with an internal link that connects one page to another page within the same website. Backlinks can also be referred to as “inbound links.”

Why Backlinks Matter

Backlinks are crucial to SEO. Each is seen by search engines as a vote of confidence from the linking websites (e.g. our philosophy blog) for the website being linked to (e.g. Wikipedia). From a user’s point of view, they also link out to related or useful information or resources on external sites.

Search engines treat backlinks as one way to discover new pages to index. They also factor backlinks heavily into their algorithms for ranking search results. When Google sees that a webpage is getting backlinks from reputable and topically related websites, it helps to build trust for that site and improve its rankings in related search terms.

Take note of the term “reputable websites,” as this does mean the quality of backlinks can and will massively impact their efficacy as a ranking signal. Having multiple backlinks from dubious sources won’t help. At worst, it can actually result in penalties. Backlinks from popular and relevant websites that people (and search engines) trust are what matters.

Remembering Relevancy

Of course, popularity is one thing but it’s also contextual to the subject and topic at hand. Our homemade philosophy blog may not have the kind of backlink portfolio as an FTSE 100 company’s website, but if it’s linking out to a fellow philosophy blogger, then it’s likely that the link will have a lot of clout because of relevancy.

Relevancy is often overlooked for site authority when link building and this is often a mistake. An SEO agency getting a backlink from a small but respected SEO blogger will have a bigger impact than getting a backlink from a reputable business blog.

Follow and Nofollow Links

In the world of links, there are two types: Dofollow and Nofollow. These two things are not visible to the end-user, but the underlying mechanics vastly differ.

Follow links are simply those without the nofollow attribute, all links are “follow” links unless they’ve specifically had the attribute added. Follow links pass link equity, allowing that linked-to page to boost its PageRank and eventually rank higher in the search engine results pages (SERPs).

Nofollow links, on the other hand, are those that do not count as points in favour of the linked-to page. They do not receive any link juice and they, ultimately, do not help rank that webpage.

Going by their definitions, it may sound logical that all backlinks should be follow links, as more follow backlinks means more votes of confidence. But that’s not always the case. Nofollow links also have their purpose, including:

Spam prevention — Nofollow links can act as a deterrent for black hat SEO practitioners who think they can game the system by adding links in the comments sections of high-traffic sites. Note that links from blog comments, social media, and forums are often marked as nofollow.
Sponsored content — Whether advertorials or press releases, links on these content are marked as nofollow because they are paid for their placement. It’s not all bad, however, as sponsored content still increases brand exposure and site traffic, especially if it’s on a highly reputable site.
Algorithm compliance — A website with a 100% dofollow link profile will be suspicious in Google’s eyes, especially in light of the Penguin update. A link profile with a balanced ratio of 50/50 or 30/70 nofollow/dofollow links works best.
Nofollow is a hint — Google announced in September 2019 that it was treating nofollow links as a hint for ranking purposes. That means that from an SEO perspective, nofollow links are still a ranking signal (albeit a reduced one).

Ranking Signals

While no one truly knows what Google’s ranking signals are (apart from the search giant itself), SEO experts have conducted their tests through the years and have come up with their own list of factors that determine Google search rankings, ranging from the proven to the controversial.

Focusing on the most important ranking signals, they reinforce the principle of having a diverse link profile with backlinks from reputable and relevant sites.

Number and Diversity

Websites with plenty of backlinks from different sources have a good chance of ranking high on Google.

Number of Linking Root Domains — The more backlinks from different domains a page has, the better its chances of ranking high in the SERPs.
Number of Linking Pages — Though not as impactful as backlinks from different domains, the number of backlinks from different pages still matter, even if they come from the same domain.
Diversity of Link Types — A link profile that is largely composed of links from one source may be considered as spammy.

Age and Authority

Backlinks from established sites definitely matter more than backlinks from sites that are barely ranking on Google.

Linking Domain Age — Aged domains factor more than new domains in Google rankings.
Backlink Age — Aged links pass on more link equity than new links.
Authority of Linking Page — PageRank has been vital in evaluating backlinks for Google Rankings and continues to be so.
Link from Authority Sites — Backlinks from Authority sites are valued more than backlinks from unknown sites.
TrustRank of Linking Site — A site’s TrustRank determines how much TrustRank its links passes on to other sites.
Links from Bad Neighbourhoods — Backlinks from seedy and spammy websites negatively impact link profiles.

Context and Relevance

The relevancy of the source and placement of a backlink matter greatly in Google search rankings.

Linking Domain Relevancy — Backlinks from sites that share the same niche as the page being linked to weigh more than backlinks from sites that don’t share the same niche.
Page-Level Relevancy — Relevant pages pass more link equity.
Contextual Links — Backlinks integrated into content are more impactful than those placed elsewhere on a page.
Links from “Hub” Pages — Backlinks from pages that are considered as go-to resources on a subject have more weight.

Not All Links Are Created Equal

Quality backlinks have a massive impact on search rankings, as numerous studies have shown. A diverse link profile, containing backlinks from popular, authoritative, and relevant domains and pages, with emphasis on the context of where links are placed within a page, are almost always associated with high ranking sites.

The freshness of content and the rate at which a page gets new links will affect link equity and rankings, with up-to-date content and pages experiencing a recent uptick of new links benefiting more from Google’s link valuation.

The phenomenon of “link echos” deserves attention as well. Basically, backlinks that no longer exist may continue to influence a page’s ranking.

It is also important to emphasise the point about nofollowed links still passing on some link equity, particularly from authority sites, making them worth pursuing even if they don’t have the same value as followed links.

These different valuations interact with one another, and Google prioritises certain factors depending on which ones come into play. If there is any takeaway from understanding these principles, it’s that there is no one type of backlink that is the end-all, be-all for getting high rankings on Google.