Verb: In grammar, a part of speech that expresses action, motion, being, suffering, or a request or command to do anything.  A verb may also show state of existence. 

The verb affirms, declares, asks or commands; as, I write; he runs; the river flows; they sleep; we see; they are deceived; they depart; they go; they come. 

The verb may also show state of existence; as in, Italy is in Europe.

The verb is the main assertive word in any sentence.

When the action expressed by a verb is exerted on an object, or terminates upon an object, the act is considered as passing to that object.  In this case, the verb is called transitive.  For example, I read the book.

When the act expressed by the verb, terminates in the agent or subject, the verb is intransitive; as in, I run, I walk, or I sleep.

When the agent and object change places and the agent becomes the instrument, the verb is passive; as in, Goliath was killed by David.

From Latin verbum (word).