Is it ensure, insure, or assure?
(SRAM) Random-access memory in which each bit of storage is a bistable flip-flop, commonly consisting of cross-coupled inverters. It is called "static" because it will retain a value as long as power is supplied, unlike dynamic random-access memory (DRAM) which must be regularly refreshed. It is however, still volatile, i.e. it will lose its contents when the power is switched off, in contrast to ROM.
SRAM is usually faster than DRAM but since each bit requires several transistors (about six) you can get less bits of SRAM in the same area. It usually costs more per bit than DRAM and so is used for the most speed-critical parts of a computer (e.g. cache memory) or other circuit.