POSIX (Portable Operating System Interface) is a family of standards that define a standardized application programming interface (API) for operating systems. The goal of POSIX is to provide a set of standards that allow software programs to be written in a portable manner, so that they can be easily compiled and run on a wide variety of operating systems. POSIX defines a set of functions and system calls that an operating system must support in order to be POSIX-compliant. These functions and system calls cover a wide range of operating system features, including file and directory operations, process and thread management, interprocess communication, and networking. POSIX also defines a standard set of header files and a standard way of defining and using data types, structures, and constants. POSIX is widely supported by many different operating systems, including Linux, Unix, and macOS, and is often used as a basis for other software standards.