It stands for "Survival Multiplayer". It's a Minecraft Survival world but in Multiplayer mode. There, you can mess around in your survival world with your friends.
An SMP is a word related to a popular Game Called Minecraft. A SMP means Survival Multi-Player (video game)
Or in simpler terms a A multi-player game with no modification nor changes to any game files.
Hey, Dave! Want to play on my SMP? I promise its gonna be FUN!!!
Or
My SMP is gonna be Chaotic place like the dream SMP.
Stands for "suck my pussy," derived from one of Sophitia's special grab move in Soul Calibur III, where she takes her opponent's head, puts it between her legs and jumps on the ground jamming her crotch in their face at high velocity. First stated by an intense brown gamer when he was losing in frustration to a stupid white guy, where he rejoiced "suck my pussy" when he won.
Now, SMP is used as the short form, synonymous to Feel It.