If you want technical info about timings, I'd do a Google search. As a consumer, all you need to know is this...
1) The lower the timings the better the performance.
2) Complete RAM timings aren't always provided, but you can usually determine the CAS latency timing.
3) CAS latency is the first number in the string of up to six. So, 2.5-3-3-6 memory has a CAS latency of 2.5.
4) The best timings for PC3200 memory are 2-2-2-5. The worst (with a few possible exceptions) are 3-4-4-8. Average, mainstream-quality timings are 2.5-3-3-6.
5) Memory faster than PC3200 generally use higher timings. DDR2 RAM often uses CAS-4.0.
6) The impact of lower CAS latency and other RAM timings on computing speed is very small. Between CAS-2.0 and CAS-3.0, you can expect to see less than a 5% performance boost.
7) Sometimes RAM advertised at a particular CAS latency only supports it at a lower bus speed. For example, DDR400 memory advertised as CAS-2.5 may only run at CAS-2.5 when operating at 333 MHz, and only at CAS-3.0 at 400 MHz. So, be careful of false claims.
Did I miss anything?