I hope this is in time.
What class is this for? Some sort of economics class?
I'll try to make this simple. If we're talking stock stock, like the stock that is traded on the New York Stock exchange, then a restricted stock unit would basically be one share of stock that cannot be sold by the owner of the stock until some sort of condition/restriction on the stock is met.
For example let's say a company's CEO gets paid with some restricted stock units. The condition on the restricted stock he's paid with is that the company would grow by a certain amount by next year. This means the CEO could not sell the stock for money until a year had passed and the company had grown by at least the amount specified on the stock. It would basically be an incentive. If the the company does well, the stock would probably increase in price and the CEO could sell the stock for a lot of money. If the company didn't do well the CEO would get nothing because he wouldn't be able to sell the stock.
_________________
I will befriend the friendless, help the helpless, and defeat... the feetless?