The label adverb clause refers to any subordinate clause which behaves as an adverb with respect to the rest of the sentence.
Definition
An adverb clause is a group of words which contains a subject and a predicate of its own. An adverb clause does the work of an adverb.
An adverb clause may express time, place, manner, cause, purpose, concession, condition or another circumstance.
Study the following examples
As soon as she finished work, Alice went home. (Here the clause ‘as soon as she finished work’ answers the question ‘when’. It therefore serves as an adverb clause of time.)
I take my mobile phone wherever I go. (Here the clause ‘wherever I go’ answers the question where. It therefore serves as an adverb clause of place.)
Susie drives better than I do. (Here the clause ‘better than I do’ says something about the manner in which Susie drives. It therefore serves as an adverb clause of purpose.)
We were late because the car broke down. (Here the clause ‘because the car broke down’ answers the question why. It therefore serves as an adverb clause of cause.)
If you get back in time, you can go with us. (Here the clause ‘if you get back in time’ expresses the condition under which something can happen. It therefore serves as an adverb clause of condition.)