“Cliclick” is short for “Command-Line Interface Click”. It is a a tiny shell/Terminal application that will emulate mouse clicks or series of mouse clicks (including doubleclicks and control-clicks) at arbitrary screen coordinates. Moreover, it lets you move the mouse, get the current mouse coordinates, press modifier keys etc.
Hence, it is a tool for automating / scripting things that cannot otherwise be scripted (for instance, using AppleScript). Other than GUI Scripting, it does not require “Access for assistive devices” to be activated in the System Preferences.
Note: If you only think of airports and gas stations when you hear the words “Shell” or “Terminal”, you will probably not need cliclick, and more importantly: you will probably not even be able to use it.