Who exactly are the proles in George Orwell's book 1984?

So, I've been reading the book 1984 by George Orwell and I am slightly confused. Who are the proles exactly. They seem like the rejects of the party but that doesn't seem right because if they really were rejects then they would just be killed off. They are also very poor. I am sooo confused! The person who gives me more details on these proles gets BEST ANSWER!