POSIX is the name for a collection of software standards based on but not limited to the UNIX system. The standards are developed by working groups of the Institute for Electrical and Electronics Engineering (IEEE); participation in these groups is open to everyone. For this and other reasons, the POSIX standards are referred to as Open Systems Standards.
The explicit goal of the POSIX effort is to promote application portability. Thus the standards specify both program and user interfaces but not implementations. Refer to www.pasc.org/standing/sd11.html#statustable for the most recent information on the status of the POSIX standards.