An expendable launch vehicle or ELV is a single-use launch vehicle usually used to launch a payload into space.
Most orbital expendable launchers are derivatives of 1950s-era ballistic missiles. Since the entire vehicle is discarded after launch, this may seem like an expensive launch method, but in practice they are cheaper than the one currently-existing partly reusable launch vehicle (the space shuttle). Most satellites are launched into orbit using expendable launchers; they are perceived as having a low risk of mission failure, a short time to launch and a relatively low cost.
Expendable launch vehicles typically consist of stages which are discarded one by one, in order not to have to carry and accelerate parts that are no longer needed, see Staging and Multistage rocket, as opposed to the as-yet theoretical single stage to orbit system. However, there is no reason in principle why an expendable single stage to orbit system would be impossible; it is just generally more efficient to use staging when the system is not meant to be recovered intact.