From Sega Retro

SRAM, in the context of Sonic hacking, stands for Saved RAM. Also known as "battery". This is usually small - about a kilobyte. As the name "battery" implies, SRAM must have power constantly running through it, or it will be erased, and the smaller it is, the longer it will last. A typical battery lasts around a hundred years, so there is no need to worry about them running out.

Sonic 3 uses SRAM to save games. Sonic 3 & Knuckles also uses SRAM, but the games are stored in the Sonic 3 cartridge, not the Sonic & Knuckles cartridge.

The term "SRAM" is sometimes used to refer to the System RAM, which is more commonly called simply the RAM.

"SRAM" can also refer to a high-speed type of RAM called "static RAM" that does not require constant refreshing as does the more common and cheaper "dynamic RAM" or "DRAM".