A continuously variable transmission (CVT) is also called a single-speed, shiftless, and stepless transmission. This transmission changes through an infinite range of gears while you drive. Other kinds of transmissions have a fixed number of gears.
CVTs deliver better gas mileage; there is no hard shifting between gears, and they give you better control on hilly terrain. The disadvantages are the higher price, noise generated by the shifting, shorter life spans, and more costly repairs.