Verb

Verbs give a sentence a bit of action.

Or, more technically (from "Webster's Revised Unabridged Dictionary (1913)")

(Gram.) A word which affirms or predicates something of

     some person or thing; a part of speech expressing being,
     action, or the suffering of action.

Note: A verb is a word whereby the chief action of the mind

     the assertion or the denial of a proposition finds
     expression. --Earle.

Verbs can be transitive, intransitive or linking. This can be thought of as different sentence patterns.

Transitive (T) verbs take objects
Intransitive (I) verbs do not take objects
Linking (L) verbs establish a link between the subject and a qualifying (describing or identifying) phrase, the "subjective complement".

A linking verb is also known as a copula.

Some verbs are used in one pattern exclusively. Others can be used in two, or in all three patterns.

(I) I grow

(T) I grow potatoes

(L) I grow angry