A verbal is a word that looks like a verb in that it implies some kind of action, but it is not functioning as a finite verb.
Verbs always have a subject; verbals never do. Verbs are often called "finite verbs" because they are limited by a subject; verbals are never so limited.
Both can take an object.
In English, there are three kinds of verbals: participles, gerunds, infinitives. They function as follows:
Gerunds are always substantives;
participles are always adjectival;
Infinitives can be adverbial, adjectival or substantival.
See also Greek participles or Hebrew participles.