(1) To write over (and therefore destroy) an existing file.
(2) A program segment that is loaded into main storage and replaces all or part of a previously loaded program segment.
(3) In Performance Tools, a graph that is placed on top of another graph so that a user can view both graphs at the same time.
(4) A collection of predefined data, such as lines, shading, text, boxes, or logos, that can be merged with variable data on a page or form while printing.
(5) The technique of repeatedly using the same areas of internal storage during different stages of a program. Unions are used to accomplish this in C and C++.