Open

Wiktionary:Open - definition
Open set (mathematics)
Open (sport) - A type of competition in tennis and golf (among others) where entry is open to all qualifiers regardless of age.
Open systems
- In science, where an open system (system theory) means a system in which matter or energy can flow into and/or out of the system, in contrast to a closed system in which no energy or matter may enter or leave the system.
- In computing, where an open system (computing) is a computer operating system that provides interoperability, portability or both, particularly Unix systems.
open vowels in Phonetics.

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