In thermodynamics, open refers to a system surrounded by a boundary across which energy, in the form of work or heat, and matter, may pass or be exchanged with its surroundings. [1] In this sense, an "open system" can have any type of interaction with its surroundings.

See also
Closed
Isolated

References
1. Perrot, Pierre. (1998). A to Z of Thermodynamics, (pg. 214). Oxford: Oxford University Press.

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