o·ver·lay¹ • v. / ˌōvərˈlā/ (past and past part. -laid) [tr.] (often be overlaid with) cover the surface of (a thing) with a coating: their fingernails were overlaid with silver or gold. ∎  lie on top of: a third screen which will overlay the others. ∎ fig. (of a quality or feeling) become more prominent than (a previous quality or feeling): his openness had been overlaid by his new self-confidence.• n. / ˈōvərˌlā/ 1. something laid as a covering over something else: a durable, cost-effective floor overlay. ∎  a transparency placed over artwork or something such as a map, marked with additional information or detail. ∎  a graphical computer display that can be superimposed on another.2. Comput. the process of transferring a block of program code or other data into internal memory, replacing what is already stored. ∎  a block of code or other data transferred in such a way.o·ver·lay² / ˌōvərˈlā/ • past of overlie.

overlay A section of code that is loaded into memory during the execution of a program, overwriting what was previously there. The loading of an overlay is under the explicit control of the programmer, and should not be confused with paging. In general several overlays are loaded into the same area of memory, “overlaying” the code already residing in that part of memory. Overlays can be thought of as a form of voluntary memory management.