UNIX, more commonly spelled Unix, is a family of operating systems that conform to the Single UNIX Specification (SUS) or that present similar behaviour to systems conforming to such a specification.
The design of a Unix systems conforms to a model of modularity, often called the "Unix philosophy", wherein each program is meant to do a specific task, and programs are meant to communicate with each other utilizing "pipes", that pass output from a program as input to another program.[1] Such flexibility has made Unix-like operating systems extremely popular among computer scientists.