Meaning – The term overlay, refers to a collection of predefined data, such as lines, shading, text, boxes, or logos, that can be merged with variable data on a page while printing.
In a general computing sense, overlaying refers to the process of transferring a block of programcode or other data into main memory, replacing what is already stored. Overlaying is a programming method that allows programs to be larger than the computer’s main memory.
Constructing an overlay program involves manually dividing a program into self-contained object code blocks called overlays laid out in a tree structure.
Example of usage – “An overlay manager, either part of the operating system or part of the overlay program, loads the required overlay from external memory into its destination region when it is needed. Often linkers provide support for overlays.”