A compendium (plural: compendia) is a concise compilation of a body of knowledge. A compendium may summarize a larger work. In most cases the body of knowledge will concern some delimited field of human interest or endeavour (for example: hydrogeology, logology, ichthyology, phytosociology or myrmecology), while a "universal" encyclopedia can be referred to as a compendium of all human knowledge. It could also be referred to as a tome.The word compendium arrives from the Latin word "compenso", meaning "to weigh together or balance". The 21st century has seen the rise of democratized, online compendia in various fields.