A measure of the quantity and quality of inbound links . Link popularity is an important factor in SEO .
Popular or relevant pages will are assumed to have more incoming(inbound) links from other websites, a type of 'vote of confidence' in the websites integrity and usefullness. Websites that are well linked within the sector rank higher than sites that are not.
In addition, link popularity is an important weapon in cracking search spam as it is difficult to manipulate artificially, and is thus less open to abuse.
Link popularity is calculated firstly by counting the amount of websites that link to yours. However, more links do not necessarily mean better rankings as search engines also measure the quality of these incoming links. If your site enjoys links from other well-linked sites then your link popularity is likely to be further improved..
What's more , some search engines, for example Google, is increasingly trying to refine their linking calculations by paying attention to the 'topic' of a link.