A gas turbine, also called a combustion turbine, is a type of continuous combustion, internal combustion engine. There are three main components:

An upstream rotating gas compressor;
A downstream turbine on the same shaft;
A combustion chamber or area, called a combustor, in between 1. and 2. above.A fourth component is often used to increase efficiency (turboprop, turbofan), to convert power into mechanical or electric form (turboshaft, electric generator), or to achieve greater power to mass/volume ratio (afterburner).
The basic operation of the gas turbine is a Brayton cycle with air as the working fluid. Fresh atmospheric air flows through the compressor that brings it to higher pressure. Energy is then added by spraying fuel into the air and igniting it so the combustion generates a high-temperature flow. This high-temperature high-pressure gas enters a turbine, where it expands down to the exhaust pressure, producing a shaft work output in the process. The turbine shaft work is used to drive the compressor; the energy that is not used for shaft work comes out in the exhaust gases that produce thrust. The purpose of the gas turbine determines the design so that the most desirable split of energy between the thrust and the shaft work is achieved. The fourth step of the Brayton cycle (cooling of the working fluid) is omitted, as gas turbines are open systems that do not use the same air again.
Gas turbines are used to power aircraft, trains, ships, electrical generators, pumps, gas compressors, and tanks.