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 is the basic condition and institution of capitalism.
Meaning of labor power
By labor power or capacity for labor we understand the set of physical and mental faculties that exist in the corporeality, in the living personality of a human being, and which he sets in motion whenever he produces use values of any kind.
Karl Marx. Capital, 1867.