"Bash is a shell, which is a program that reads commands and executes them. Sometimes, the commands that Bash reads come directly from the keyboard as you type them. When this happens, we say that Bash is an interactive shell. If you've ever logged into a UNIX system, then you've used an interactive shell. Bash is the default interactive shell of the GNU/Linux system (and you might also find it installed on commercial UNIX systems). Sometimes, the commands that Bash reads come from a file called a shell script. When this happens, we say that Bash is a non-interactive shell. In this case, Bash reads each line of the script file from top to bottom, executing each command as if it had been typed on the keyboard." (Liunx Review)