Epigenetics is a term that has changed its meaning with the increasing biological knowledge on developmental processes. However, its current application to stem cell biology is often imprecise and is conceptually problematic. This article addresses two different subjects, the definition of epigenetics and chromatin states of stem and differentiated cells. We describe mechanisms that regulate chromatin changes and provide an overview of chromatin states of stem and differentiated cells. Moreover, a modification of the current epigenetics definition is proposed that is not restricted by the heritability of gene expression throughout cell divisions and excludes translational gene expression control.