Also known as "locality in space" and "spatial locality," it refers to the fact that most instructions in a program are in routines that are executed over and over, and that these routines are in a reasonably confined area. It also refers to data fields in close proximity to each other.
This is the principle behind memory and disk caches, in which data or instructions are placed in higher-speed memory and get read many times before the memory is overwritten by another set. See
cache.