In all programming languages and command line interfaces, certain words, phrases, and codes that are entered in the program--or at a line prompt--instruct the computer's processor to perform specific functions. In DOS, for instance, the command "CLS" instructs the computer to clear the screen of all information, leaving only a new command prompt ready for the next instruction. In the programming language BASIC, the command "RETURN" is used at the end of a short set of instructions nestled within a program (also termed a subroutine) to cause the computer to return to the point in the program where it was asked to run the subroutine. The "CLS" and "RETURN" commands are words that, when entered alone, generate a response from the computer. Not all commands, however, perform a function on their own.

For example, when formatting a disk from a computer's DOS prompt, the command "FORMAT" is used...