What is a SMP server?
SMP Servers are also known as Survival Multiplayer servers. SMP usually refers to a Minecraft server that is set to survival mode, with the focus not on solo gameplay, but instead playing with a group of other Minecraft players.
What is the best Minecraft SMP server?
Since there are many Minecraft SMP servers out there, it's generally good idea to check out top SMP servers and see if you like them, since different people have different tastes and not all SMP servers are the same.