A turboshaft engine is a form of gas turbine which is optimized to produce shaft power, rather than jet thrust.
In concept, turboshaft engines are very similar to turbojets, with additional turbine expansion to extract heat energy from the exhaust and convert it into output shaft power. They are even more similar to turboprops, with only minor differences and often a single engine is sold in both forms.
Turboshaft engines are commonly used in applications which require a sustained high power output, high reliability, small size, and light weight. These include helicopters, auxiliary power units, boats and ships, tanks, hovercraft, and stationary equipment.