Meaning of specific impulse

specif'ic im'pulse

Pronunciation: [key]
— Rocketry. Rocketry.
  1. a measure, usually in seconds, of the efficiency with which a rocket engine utilizes its propellants, equal to the number of pounds of thrust produced per pound of propellant burned per second.
  2. the specific impulse that a given combination of propellants would produce in an ideal rocket engine providing complete combustion, no friction losses, and no lateral expansion of the exhaust.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.