Here's my understanding of BHP:

When testing an engine on a dynomometer, a device (called a brake) applies a load to the engine to keep it at a particular RPM (typically at full throttle). A load cell/strain gauge measures the amount of force applied by the brake. By taking the RPM and force applied by the brake, horsepower is derived. That is where Brake HorsePower comes from.
_________________________
60GB Amber 10GB Blue