What is the definition of SACD -noobQ-

I couldn't find any definitions using the site search or a few mfgr web sites. I assume it is Stand Alone CD (player) after viewing a rear panel? Any special CD disk reqmts? Rediscovering my audiophile hobby after navy retirement. Also saving to purchase new DVD/CD player. My Stuff: Carver: TFM-35x, DPL-33, CT-23, (SDA-360 broken). Sony: TC-WE435, SEQ-711, Pioneer RT-707. Speakers...nevermind. lol.