Specific thrust

Specific thrust is the thrust per unit air mass flowrate of a jet engine (e.g. turbojet, turbofan, etc.) and can be calculated by the ratio of net thrust/total intake airflow.

Low specific thrust engines tend to be more efficient of propellant (at subsonic speeds), but also have a lower effective exhaust velocity and lower maximum airspeed. Engines considered to have high specific thrust are mostly used for supersonic speeds, and extremely high specific thrust engines can achieve hypersonic speeds.