Simple Definition:

A verb is a word that describes an action [something that someone does], occurrence [something that happens], or state of being [the state of something]. Verbs are used to show what someone or something does [performs], what happens to them, or how they are. For example, in the sentence "She runs every morning", the verb "runs" describes the action that "she" performs. In "The sun rises in the morning," the verb "rises" describes the occurrence of the sun moving up. In "He is happy," the verb "is" shows his condition.

Very Simple Definition:

A verb is a word that shows what someone or something does, or the state or condition of a thing or person. For example, in the sentence "She runs every morning", the verb "runs" shows what "she" does. In "The sun rises in the morning," "rises" shows something happening. In "He is happy," "is" shows how he feels.