You are referring to RAM I presume.
The number refers to the cycles or the speed at which the memory runs, 133 being a highr speed. You can usually use 133 in a motherboard designed for 100 but it will run at the lower speed.
Dell XPS 13 9370 (2018) review
The art of 'British' pulp fiction
Best password managers for Mac
TV & streaming : comment regarder le Tournoi des Six Nations 2018 ?