Noun
Examples
"because" in "I'm staying in because it's raining."
subordinating conjunction (plural subordinating conjunctions)
(grammar) A word that appears at the beginning of a subordinate clause and establishes its nature.
Coordinate term: coordinating conjunction
A dependent clause also normally contains a subordinating conjunction (or in the case of relative clauses, a relative pronoun or phrase containing one). Source: Internet
Another type of dependent clause with no subordinating conjunction is the conditional clause formed by inversion (see below). Source: Internet
Dependent clauses The syntax of a dependent clause is generally the same as that of an independent clause, except that the dependent clause usually begins with a subordinating conjunction or relative pronoun (or phrase containing such). Source: Internet