SDRAM
Synchronous dynamic random access memory delivers bursts of data at high speeds using a synchronous interface. Its is actually SDR SDRAM (single data rate SDRAM) but is usually used to referred to as just "SDRAM."

PC100
The PC100 specification defines the requirements for SDRAM modules used on 100MHz FSB motherboards.

PC133
The PC133 specification details the requirements for SDRAM modules used on 133MHz FSB motherboards. PC133 SDRAM can be used on 100MHz FSB motherboards but will not yield a performance advantage over PC100 memory at 100MHz.

FSB
Front Side Bus - The main highway for data in a PC. It connects the processor, chip set, DRAM, and AGP socket. FSB is described in terms of its width in bits and its speed in MHz.