A shell extension allows one to extend the abilities of the shell. For example, in Windows Explorer the program is designed primarily to show you the contents of your system. An extension could be applied to add information (tabs) to a dialog box to show information that was not previously available.

A shell extension allows one to extend the abilities of the shell. For example, in Windows Explorer the program is designed primarily to show you the contents of your system. An extension could be applied to add information (tabs) to a dialog box to show information that was not previously available.

A rostrum on a crayfish is an extension of its shell. This part is used for extra protection.

Shell programs should normally end in .sh, but it is not a requirement.