Definition of CLI

A form of interface between the operating system and the user in which the user types commands, using a special command language. Although systems with commandline interfaces are usually considered more difficult to learn and use than those with graphical interfaces, command-based systems are usually programmable; this gives them flexibility unavailable in graphics-based systems that do not have a programming interface.

A specification describing how applications written in multiple high-level languages may be executed in different system environments without the need to rewrite the applications to take into consideration the unique characteristics of those environments.