When shopping for computer RAM you'll likely notice that in the specifications for each is a CAS (Column Access Strobe) Latency number, like CL16 on many 3200MHz DDR4 RAM kits.
Basically, the CAS latency, or CL, is an indication of the time it takes for your memory controller to get a particular piece of data ready to access from the RAM, so lower numbers are generally more desirable.
It's important to note the number appearing after CL, as in CL16 for example, is just one part of the whole process, and the measurement of time in these processes are NS (nano seconds) being used, which is unit of time equal to one thousand-millionth of a second.
The second part of the process is the RAM speed which refers to the volume of data the RAM can send and receive from your CPU. This is measured in MHz. To expand on this a little more, without going too deep, if I look at 3000MHz CL16 DDR4 vs 3200MHz CL16 DDR4 the 3200MHz kit is faster because it has a higher peak MHz, even though they are both CL16.
On the PB Tech Website, when you are shopping for RAM, once you choose the type (Desktop RAM, Laptop RAM or Server RAM) you can filter the results as shown below to find specific CL, MHz, sizes and more.