POSIX stands for Portable Operating System Interface. It is a family of standards developed by the IEEE Computer Society to define a common application programming interface for Unix-like operating systems, so that programs can move between systems with little or no change.
The first standard in the family, IEEE Std 1003.1-1988, was published in 1988 and approved by the IEEE Standards Board on 22 August 1988. By the 1980s many divergent Unix variants existed, including System V and the BSD line, each with subtle differences. POSIX.1 distilled a common core from these systems, specifying base services such as processes, files, and input and output.
Standardizing the interface meant a developer could write to POSIX rather than to one specific vendor’s Unix, and reasonably expect the program to compile and run elsewhere. This portability was important to governments and large buyers who did not want to be locked to a single supplier.
The United States government adopted POSIX as Federal Information Processing Standard 151, reinforcing its reach. Later editions, including alignment with The Open Group’s Single UNIX Specification, extended and revised the standard, but the 1988 publication established the baseline that still shapes Unix, Linux, and macOS interfaces today.