what exactly is anchor text in seo?

where it matters for seo is the mix. on links you build from other sites, if nearly all of them use the exact keyword you want to rank for, it looks manufactured and can count against you. real link profiles are mostly your brand name, the bare url, and loose phrases. internal links on your own site are different - be as descriptive as you like there.

the clickable words of a link. a link reading "keyword research guide" tells the reader and google what the page on the other end is about.