POSIX

The Portable Operating System Interface (POSIX; IPA: /ˈpɒz.ɪks/) is a family of standards specified by the IEEE Computer Society for maintaining compatibility between operating systems. POSIX defines both the system and user-level application programming interfaces (APIs), along with command line shells and utility interfaces, for software compatibility (portability) with variants of Unix and other operating systems. POSIX is also a trademark of the IEEE. POSIX is intended to be used by both application and system developers.
— Wikipedia

References

• The Open Group Base Specifications Issue 7, 2018 edition
• A Guide to POSIX | Baeldung on Linux
• standard - What exactly is POSIX? - Unix & Linux Stack Exchange