Open may refer to:

In philosophy

• Openness, term being used to define the basis of how various groups and organizations operate.

In mathematics

• Open problem, a well-defined problem with no known solution in science and mathematics
• Open set, set in topology and related fields of mathematics
• Opening, an operator in mathematical morphology

In music:

• Open (album), 2004 album by Shaznay Lewis
• Open (band), Australian pop/rock band

In other fields:

• open (application), Nextstep & Mac OS X command line application that opens its argument(s) in the GUI as if the user had double clicked
• Open circuit, in electronics, the absence of a load through which electric current would flow.
• Open-source software, computer software modifiable by all, where users are treated as co-developers.
• Open (magazine), a lifestyle Mexican publication.
• Open (sport), type of competition in tennis and golf where entry is open to all qualifiers regardless of age
• Open vowel, vowel sound of a type used in most spoken languages
• Open...., the original interactive television service on BSkyBs Sky Digital platform
• Organization of Pakistani Entrepreneurs of North America, inclusive, not-for-profit organization.
• Open Season, a movie made in Sony Animation.
• the C POSIX library function open(2), defined in fcntl.h and used for C file input/output

[ See also

• Open-ended
• Open mind
• Open system
• Closed