- shell: not precise. Interface that allows you to interact with the operating system: create files, read files, manage sound, etc. more nicely than in machine code. Can be used for graphical interfaces, like a Gnome shell, sometimes it is just the command line where you type and see text only.
- command line: not precise. Could be any shell that uses text only to interact with the OS, such as the Bourne Shell, bash, C shell, etc.
- Bourne shell (sh): an old important shell that inspired Bash (bash). Has a specific language to it.
- Bourne again shell (bash): default shell nowadays. Obviously inspired in the Bourne Shell. Also uses a specific programming language, which is very close to that of the Bourne shell.
- C Shell (ssh): another influential shell, whose programming language looks more like c than bash does.
- and the list goes on…