Anchor text
As was demonstrated in the Internal Links section, the wording that is used to link to a particular site is one of the key factors for the search engines in determining what a particular page is about.
The ideal scenario for inbound links is as follows:
Site A is counted as an "authority" site for the same subject as that which Site B is about - e.g. "art and design"
Site A links to Site B, using the phrase "art and design"
Site B thus receives the ultimate "vote" - a reference from a relevant, "authority" site, that describes Site B as being about its target search phrase.
Anchor text links are hugely important for achieving good rankings in the SERPs.