An adverbial clause is a clause that functions as an adverb to modify a verb. It provides information about place, time, cause, purpose, concession, or condition. Adverbial clauses are introduced by subordinating conjunctions like after, before, when, because, if, although, while, as, as soon as, since, until, whenever, where, and whereas. They provide context about when, where, why, how, or under what condition something occurred.