A nonfinite verb is a verb that does not function as the predicate verb in a clause. While some nonfinite verbs take the form of past or present participles, they are generally not inflected—that is, they don’t have mood, tense, number, aspect, gender, or person.
The opposite of a nonfinite verb is a finite verb, which does serve as a predicate verb—for example, the verbs in She walks, He sings, and I went.
A gerund is an -ing verb that functions as a noun—for example:
Are you into reading?
Sailing is my favorite sport.
When the same words are used as adjectives, they are participles.
Infinitives are noninflected verbs that are often preceded by to. They may function as adverbs:
I struggle to understand.
They may function as nouns:
To read is good for the mind.
And they may function as adjectives:
I don’t have time to eat.
Participles are -ed and -ing verbs that function as adjectives—for example:
The sleeping cat is brown.
The freshly picked tomatoes look delicious.
I am going to the store.
The kids were dropped off at school.
A nonfinite clause is a dependent clause whose main verb is nonfinite. It may function as a noun, adjective, or adverb:
Your calling me was very considerate.
The firetruck, blaring its siren, sped down the road.
We wanted to bring you a present.