Answer:
Subordinating conjunction
Step-by-step explanation:
Subordinating conjunctions are words that make clauses dependent, that is to say, clauses that can not stand alone as a sentence because they do not express a complete thought on its own.
The functions of this type of conjunction are to introduce a subordinate (or dependent) clause and to join subordinate clauses to independent clauses by providing a transition between these two. Some examples of this type of conjunctions are after, since, although, as long as, because, before, even, even though, in order that, wherever, unless and until.
Here's an example of a sentence containing one:
Since advertisements are sometimes misleading, read labels carefully.
In this example, the clause underlined is a dependent clause, and the one that is not underlined is an independent clause. As you can see, the subordinating conjunction "since" introduces the clause and makes the clause dependent because if "since" wasn't placed there, the clause would express a complete thought on its own.