This is a group of related words with a subject and predicate that acts to modify a verb adjective or adverb?

The description refers to an adverbial clause. An adverbial clause is a group of related Words that contains a subject and a predicate and provides additional information about a verb, adjective, or adverb in a sentence. It typically answers questions such as when, where, why, or how something occurs. For example, in the sentence "She sings beautifully when she is happy," the clause "when she is happy" modifies the verb "sings."