Generally a small block of fast memory that sits between either 1) a smaller, faster chunk of memory and a bigger, slower chunk of memory, or 2) a processor and a bigger, slower block of memory. This is to provide a bridge from something that's comparatively very fast to something that's comparatively slow. Most computers have cache memory that holds some of the information from main memory. When the processor needs the information it takes it from the faster cache instead of the slower main memory. Cache memory GREATLY increases the speed of a computer by storing data that is most often accessed. See Cache Buffer