ram has speed and timings, see here for the example
http://www.newegg.com/Product/Product.aspx?Item=N82E16820227478

Its speed is 1333MHz and its timings are 7-7-7-20 which is quite good, the first number of the timings is the CAS, lower is better as it refers to how many clock cycles it takes to access a chunk of data, normally DDR3 has timings of 9-9-9-24 so anything lower than that is considered to have low or tight timings.

You will also see ram advertised just listing its CAS Latency generally in the form CL9 or CL7, again lower is better here.