• Open set (mathematics)
• Open problem in science and mathematics, a well-defined problem with no known solution
• 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
• Open... was the original interactive television service on BSkyBs Sky Digital platform
• open (application)

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