Open system (systems theory), a system where matter or energy can flow into and/or out of the system, in contrast to a closed system, where energy can enter or leave but matter may not
Open system (management science), in management science a system that is capable of self-maintenance on the basis of throughput of resources from the environment
Open system (computer science), in the computer sciences a collection of interacting software, hardware, and human components with well-defined, publicly available interfaces maintained by a consensus process
Open system (computing), one of a class of computers that provides some combination of interoperability, portability and open software standards, particularly Unix and Unix-like systems