Why not just go to Intel, they make the things?
Front Side Bus Speed
The speed of the bus that connects the processor to main memory (RAM). As processors have become faster and faster, the system bus has become one of the chief bottlenecks in modern PCs. Typical bus speeds are 400 MHz, 533 MHz, 667 MHz, and 800 MHz.
Clock Speed
The speed at which the processor executes instructions. Every processor contains an internal clock that regulates the rate at which instructions are executed. It is expressed in Megahertz (MHz), which is 1 million cycles per second or Gigahertz (GHz), which is 1 billion cycles per second.
L2 Cache
The size of 2nd level cache. L2 Cache is ultra-fast memory that buffers information being transferred between the processor and the slower RAM in an attempt to speed these types of transfers.
Here's a link to a processor comparison chart, this has links to a Glossary I got this from. There's also links to the various processor types
Compare Desktop Processor Specifications
The reason that Core Duo and Core 2 Duo processors have lower processor clock speeds is that the older Pentium 4 got horribly hot, causing even higher power consumption and failures.
The new Core Duo design allows the operation of two (or more) cores in one processor, effectively doubling performance while running at the same speed. This also has the benefit of splitting the operation of programs onto different cores, allowing multiple programs to run simultaneously on different cores which can improve real operation even more.
Intel® Dual-Core Technology
Processors with Quad cores already exist and others will be coming. Since only a portion of the separate cores needs to be duplicated (registers, cache) and much can be shared, the size of the processor doesn't grow linerally, and larger processors are easier to cool than fast smaller ones.
Bitman