The staged combustion cycle, also called topping cycle or pre-burner cycle, is a thermodynamic cycle of bipropellant rocket engines

Rocket engine

A rocket engine, or simply "rocket", is a jet engineRocket Propulsion Elements; 7th edition- chapter 1 that uses only propellant mass for forming its high speed propulsive jet. Rocket engines are reaction engines and obtain thrust in accordance with Newton's third law...

. Some of the propellant is burned in a pre-burner and the resulting hot gas is used to power the engine's turbines and pumps. The exhausted gas is then injected into the main combustion chamber, along with the rest of the propellant, and combustion is completed.

The advantage of the staged combustion cycle is that all of the engine cycles' gases and heat go through the combustion chamber, and overall efficiency essentially suffers no pumping losses at all.