A rocket engine is a type of propulsion system that generates thrust to propel a rocket into space. It works by expelling gas at high speed, following Newton's third law of motion, which states that for every action, there is an equal and opposite reaction. Rocket engines can be powered by liquid or solid fuels, each with its own advantages and disadvantages. These engines are crucial for space exploration, enabling missions to reach destinations like the Moon or Mars. They are also used in various applications, including launching satellites into orbit and powering space shuttles.