The average (mean) pressure which, if imposed on the pistons uniformly from the top to the bottom of each power stroke, would produce the measured (brake) power output.

Alternative form of fraternal birth order effect

The scientific observation that a man's statistical probability of being homosexual increases with the number of older brothers he has.

plural of brake mean effective pressure

(physics) A physical phenomenon in which a change in the magnetic moment of a free body causes the body to rotate, as a consequence of the conservation of angular momentum.