A backlink is an external link that points to a website or, more precisely, a web page. The benefits of backlinks are twofold :
- They can be a source of traffic when used by visitors to the referring websites where they are found
- They promote search engine optimization and ranking in Google results.
This second effect is often considered the most important in the long term, the number and especially the quality of backlinks are indicators of the popularity of a website, which are strongly considered by Google and other search engines when indexing and ranking websites in response to a search query. The backlink is logically considered a "vote" or "certificate of quality" for the website it links to.
Originally, search engines considered inbound links using a quantitative approach. The more inbound links a site had, the more it was favored in search results. As practices to more or less artificially multiply inbound links have multiplied, search engines are using an increasingly qualitative approach to consider these links. In particular, Google has developed its Penguin filter to combat artificial links.
The different elements taken into account by search engines to evaluate the value of backlinks include.
- the quality and trust of the sites where they are found
- the thematic proximity of the sites where they can be found
- the number of other external links on the site
- the way the link is written (see anchor text)
- the position of the link within the page (contextual links and structural links)