An isolated system is a physical system that does not exchange matter or energy with its surroundings. This means that the total energy and mass within the system remain constant over time. An example of an isolated system is a perfectly sealed container that prevents any heat or particles from entering or leaving. In thermodynamics, isolated systems are important for understanding the principles of energy conservation and entropy. The concept helps scientists analyze processes without external influences. Real-world examples are rare, but the universe itself can be considered an isolated system, as it contains all matter and energy without external interaction.