Set of physical and intellectual capacities that a person applies when generating use values in a productive process. Its sale for a certain time in the market as a commodity by those who cannot produce by themselves and have no other commodity to sell -the proletariat-, is the basic condition and institution of capitalism.
By labor power or labor capacity we understand the set of physical and mental faculties that exist in the corporeality, in the living personality of a human being and that he puts in motion when he produces use values of any kind.
Karl Marx. Capital, 1866.