When you agree to pay a car dealer for the use of a new car during a set period of time for a set amount of money and you have to return it at the end of that period of time, you are leasing a car.
Vehicle leasing is the leasing (or the use) of a motor vehicle for a fixed period of time at an agreed amount of money for the lease. It is commonly offered by dealers as an alternative to vehicle purchase but is widely used by businesses as a method of acquiring (or having the use of) vehicles for business, without the usually needed cash outlay. The key difference in a lease is that after the primary term (usually 2, 3 or 4 years) the vehicle has to either be returned to the leasing company or purchased for the residual value.