A software program for initiating the operation of a computer.

The function of the program is to set up the input and output (I/O) devices and load the OPERATING SYSTEM from a disk, cassette, or built-in ROM.

Because the computer gets itself up and going from an inert state, it could be said to lift itself up "by its own bootstraps" -- this is where the term Boot originates.

Other computer systems are also said to have a bootstrap. For example when writing a compiler written in the language that the compiler compiles (think about it for a second), it is necessary to have either a CrossCompiler or a BootStrap -- a program written in a different language (assembler in the worst case scenario) which can be used to compile a cut-down version of the compiler initially. Of course, once even a bare-bones version of the new compiler runs on the new platform it can be used to compile more sophisticated versions of the compiler. Given the choice, cross-compilation is usually preferred.