The answer is: subordinate clause.
Subordinate or dependent clauses begin with a relative pronoun (like who or which) or a subordinate conjunction (such as although or because). They cannot stand on their own because they do not indicate a total idea. Consequently, they need to join at least one independent clause in order to make sense.
In the following example the subordinate clause is in bold:
Although the weather was hot, we didn't go to the beach.