brake horsepower

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. The actual or useful horsepower of an engine, usually determined from the force exerted on a friction brake or dynamometer connected to the drive shaft.

Wiktionary

1. n. The useful horsepower of an engine as measured at its drive shaft.

GNU Webster's 1913

1. the net effective power of a prime mover, as a steam engine, water wheel, etc., in horse powers, as shown by a friction brake. See Friction brake, under Friction.