POSIX (an acronym for "Portable Operating System Interface") is a family of standards that specifies the behaviour of Unix-like operating systems.
These standards define:
- A standard operating system interface and environment
- A programming API for the C programming language
- The behavior of a command interpreter (or "shell")
- The behavior of common utility programs invocable from the shell
The current set of POSIX standards is available online.
POSIX is a trademark of the IEEE.