If a clause can stand alone as a sentence, it is an independent clause, as in the following example:

Independent

the Prime Minister is in Ottawa

Some clauses, however, cannot stand alone as sentences: in this case, they are dependent clauses or subordinate clauses. Consider the same clause with the subordinating conjunction "because" added to the beginning:

Dependent

when the Prime Minister is in Ottawa

In this case, the clause could not be a sentence by itself, since the conjunction "because" suggests that the clause is providing an explanation for something else. Since this dependent clause answers the question "when," just like an adverb, it is called a dependent adverb clause (or simply an adverb clause, since adverb clauses are always dependent clauses). Note how the clause can replace the adverb "tomorrow" in the following examples:

adverb

The committee will meet tomorrow.

adverb clause

The committee will meet when the Prime Minister is in Ottawa.

Dependent clauses can stand not only for adverbs, but also for nouns and for adjectives.