CLI is a command line program that accepts text input to execute operating system functions
A linux user might be more acquainted to using commands in a terminal
Such commands are interfaces of underlying programs, which receive input from a user on the command-line using such interfaces
Following are some common common commands of Linux, Mac and Windows :
cd - Change directory command, which allowsa user to change the current working directory mkdir - used to create a directory or folder rmdir - used to remove a directory or folder ls(linux, mac), dir(windows) - lists the files and folders of a directory pwd(linux, mac), cwd(windows) - prints(i.e. displays) the (current) working directory cp(linux, mac), copy(windows) - copy a file or directory to another directory (or same directory with a different name)