CVT stands for Continuously Variable Transmission. They are the most efficient and simple gearbox type - essentially a single gear that isn't fixed, altering its shape depending on how the car is being driven. The upside is that they are reliable, smooth around town and usually efficient (especially when mated to hybrid systems). The downside is that when you demand more or full power the revs soar and stay high until you stop, which can be noisy and frustrating. Newer CVT gearboxes are much better in this respect, however.