Internal link
An internal link is a link from one page of a site to another page on the same site, used to pass authority, establish topical relationships and give crawlers a path through the site.
Internal linking is the highest-leverage on-site work available because it costs nothing and needs no external cooperation. The constraint is that a useful link needs a sentence that already exists and already shares terms with the target. Anywhere else, adding the link means writing a new sentence.
Anchor text carries the signal. Repeating the same exact-match anchor across a site is where over-optimisation shows up first.
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