What do you call a group of words that acts like an adverb?

noun phrase

prepositional phrase

adverbial clause

adverbial phrase

The correct answer is adverbial clause.

An adverbial (adverb) clause is a group of words that function as an adverb in a sentence.

Adverb clauses add information that elaborates on when, where, why, how the action in the sentence takes place.

An adverb clause must contain a subject and a verb to be complete.

An adverb clause can be used at the beginning of a sentence:

Before you do your homework, go and see your sister.

They can also be placed at the end of a sentence:

The day felt lonely because nobody came to visit me.

Adverbial clause should be the answer