Dictionary.net

(Or cache block) The smallest unit of memory thancan be transferred between the main memory and the cache.Rather than reading a single word or byte from main memory ata time, each cache entry is usually holds a certain number ofwords, known as a "cache line" or "cache block" and a wholeline is read and cached at once. This takes advantage of theprinciple of locality of reference: if one location is readthen nearby locations (particularly following locations) arelikely to be read soon afterward. It can also take advantageof page-mode DRAM which allows faster access toconsecutive locations.