A word or phrase which gives information about when, how, where, or in what circumstances something happens. It can be an adverb, a group of words with an adverb as a main word, or a prepositional phrase. E.g. They looked passionately at each other. She performed well at the Peninsula Hotel yesterday.
In grammar an adverbial is a word (an adverb) or a group of words (an adverbial phrase or an adverbial clause) which modifies or tells us something about the sentence or the verb. The word adverbial is also used as an adjective, meaning 'having the same function as an adverb'.