A conjunction is the glue that holds words, phrases and clauses (both dependent and independent) together. There are three different kinds of conjunctions––coordinating, subordinating, and correlative––each serving its own, distinct purpose, but all working to bring words together.
Read more at http://grammar.yourdictionary.com/parts-of-speech/conjunctions/what-is-a-conjunction.html#da4rfFFk2fKXV6fj.99