The socket pertains to the CPU. It's what the CPU is placed into on the motherboard. All CPUs fit in a certain socket. For example, the newer AMD Athlon 64's go in a socket 939. So, if you have an Athlon 64, you will want a socket 939 motherboard. The newer Intel P4's go in a socket LGA775 (Socket T).
so if my current processor is in a mobo with a 478 socket, i need to get a new one with the same socket number, right? (or tell me what do you guys need to know to see which MoBo would be better?)