Recently I've been researching SMACSS by Johnathan Snook and the BEM Methodology by Yandex as well as examing my own style of crafting CSS. I've started adopting an approach based on SMACSS that uses the Base, Layout, Module, State approach for structuring my CSS, though I'ved expanded on the concept of modules based on my research into the BEM methodolgy. I've started using a pattern which I refer to it as Module, Subcomponent, Modifier.
The concept of modules is the same concept of modules described in SMACSS. So if your fimiliar with SMACSS, you already know what modules are.