Restricted stock - “The company issues common stock to the employee and puts some restrictions on the stock. The restrictions typically include a vesting schedule and some limits on how the stock can be sold once it is vested.”
RSU - “A RSU is a promise to issue restricted stock upon the acheivement of a certain vesting schedule. It is a lot like a stock option but you do not have to exercise it. You simply get the stock like a restricted stock grant.”
http://www.avc.com/a_vc/2010/11/employee-equity-restricted-stock-and-rsus.html