An open system may refer to more than one thing:

• In the physical sciences, an open system (system theory) is a system that matter or energy can flow into and/or out of, in contrast to a closed system, which no energy or matter may enter or leave. See also closed system.
• In computing, an open system (computing) is a computer operating system that provides interoperability, portability or both, particularly Unix systems.
• In management science, an open system (system theory) is a system that takes in (raw materials, capital, skilled labor) and converts them into goods and services (via machinery, human skills) that are sent back to that environment, where they are bought by customers. Contrarily a closed system is self contained, does not interact with its external environment and risks to experience entropy.