Jet engines are a type of internal combustion engine that propel aircraft by expelling jet streams of gas. They work on the principle of Newton's third law, where the action of expelling gas results in a reaction that pushes the aircraft forward. These engines are crucial for modern aviation, providing the necessary thrust to lift and sustain flight. There are various types of jet engines, including turbojets, turbofans, and turboprops, each designed for specific applications. The efficiency and power of jet engines have evolved significantly, making air travel faster and more accessible. Innovations in materials and design continue to enhance their performance and reduce environmental impact.