Who are "the proles"? What does Winston mean when he says, "if there is hope it lies in the proles"?

Proles are the members of the working class. In order for things to change, the proles have to step-up and stand-up for themselves. They have the power to create change due to their large number, but ignorance and complacency dashes hopes for a better life. Winston is correct in saying they are the hope of the future because with numbers.... there will never be change.