shell or command prompt
The single character or set of characters that the UNIX shell displays for which a user can enter a command or set of commands.

shell preprocessing
This describes actions taken by the shell to manipulate the command line before executing it. This is when filename, variable, command, and arithmetic substitution occur (as covered in Chapter 8, “Substitution”).

shell script
A program written using a shell programming language like those supported by Bourne, Korn, or C shells. In general, a script contains a list of commands that are executed noninteractively by the shell.

shell variable
A special variable that is set by the shell and is required by the shell in order function correctly.

signal
Software interrupts sent to a program to indicate that an important event has occurred. The events can vary from user requests to illegal memory access errors. Some signals, like the interrupt signal, indicate that a user has asked the program to do something that is not in the usual flow of control.

signal handler
A function that executes when a signal is received by a shell script. Usually signal handlers clean up temporary files and then exit.