Numerical expression of importance (authority) a web resource in the eyes of a search engine.

Determined by assessment reference mass site. It is important not so much quantity incoming links, like their quality, which is characterized by a similar topics and authority donor sites.

Long search engine Google appropriated his “company” IC called PageRank, but now it is no longer updated.

But y Yandex there are two options: tis (thematic) and vice (weighted).

High citation indexes have a positive effect on web resource positions in searchable issues, and also appreciated on link exchanges (if it comes to the IC site of the donor).