some vocabulary (source: wikipedia)

A shell (unix-shell) is a command-line interpreter or shell (=Hülle) that provides a command line user interface for Unix-like operating systems. The shell is both an interactive command language and a scripting language, and is used by the operating system to control the execution of the system using shell scripts.

Bash stands for Born Again SHell and is a unix shell and command language written by Brian Fox (improved version of the shell).

Terminal (terminal emulator): programm to interact with the shell (bash).

TUI: textbased user interface (for example a terminal emulator or vim when running in a terminal).

GUI: graphical user interface -> what most users are used to.