A copular verb.    From Wordnet, Princeton University. 

In the Oxford English Grammar, Sidney Greenbaum writes: "If the copular verb is BE and if the subject predicative identifies the subject, the subject and subject predicative can change places.".    From Wordnik.com.  [On all and all] Reference

For the grammar geeks out there, I'll quote Algeo's British or American English on the topic, "A group of copular verbs (...) have predominantly adjectival complements in common-core English, but also have nominal subject complements in British more frequently than in American.".    From Wordnik.com.  [separated by a common language] Reference