1. A substitute component that is employed temporarily in a program so that progress can be made, e.g. with compilation or testing, prior to the genuine component becoming available. To illustrate, if it is required to test the remainder of a program before a particular procedure has been developed, the procedure could be replaced by a stub. Dependent upon circumstances, it might be possible for this stub always to return the same result, return values from a table, return an approximate result, consult someone, etc.