RSU == the right to be GIVEN a dollar amount equivalent of shares at a future date. No strike price, which is great. And if you're at a public company, this is a liquid asset now, so while you now owe taxes on this thing you were just given, you can also sell it to pay those taxes. Relatively risk free. If you're a private company however, then RSUs are the right to be given something at a fixed date that has immediate tax implications with no liquidity.