Unix-like

A Unix-like operating system is one that behaves in a manner similar to the UNIX system.

The Open Group, which owns the UNIX trademark, considers "UNIX-like" to be a usage problem, and believes that a better alternative term would be the term "POSIX-conforming system." However, the term POSIX-conforming system has its own problems. For example, there are systems which conform to at least the key POSIX standards (e.g., Microsoft Windows) and can claim to be POSIX-conforming, but nevertheless they are not Unix-like and thus many applications written to run on Unix will not run on them.

Often used to refer to the open source Unix like systems, Linux, FreeBSD, OpenBSD, NetBSD and HURD