Backlash
Backlash, also referred to as play, lash or slop, is a gap between two parts in a mechanism causing lost motion and increased wear. Some amount of backlash is unavoidable in nearly all reversing mechanical couplings, although its effects can be negated or compensated for. In many applications, the theoretical ideal would be zero backlash, but in actual practice some backlash must be allowed to prevent jamming. There are cases where some backlash is desired to allow for lubrication, manufacturing errors, deflection under load, and thermal expansion.
