Specific impulse (abbr. isp) was a measurement for rating the performance of a rocket engine. This measurement gives information on the number of pounds or kilograms of thrust that are derived from the consumption of a pound or kilogram of propellant in one second.
The semi-solid propellant moyerite (synthetic) and the hypergolic propellant gronerium compound 3983 had a low specific impulse of 450 isp. These propellants was used in ullage thruster devices and emergency jettison thrusters. (TNG: "Night Terrors")