Object omes are various omes that describe the whole set of something that are mostly static entities. Genome and Proteome are object omes.
While action omes are omes that describe biological processes and activities. Expressome has action ome meaning as well as object ome meaning. Expressome can mean anything that are produced by the activity of cell expression as RNA. Protein, and even ligands produced in cells. So, expressome is somewhat based on the activity as well as the activities results (expressed RNA, for example). However, the distinction between object ome and action ome can not be strict as there are numerous borderline cases.