What is the meaning of Horsepower?

Power derived from the motion of a horse.

A nonmetric unit of power (symbol hp) with various definitions, for different applications. The most common of them is probably the mechanical horsepower, approximately equal to 745.7 watts.

A metric unit (symbol often PS from the German abbreviation), approximately equal to 735.5 watts.

Strength.

Source: wiktionary.org