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 a specific field of human interest or endeavour (for example: hydrogeology, logology, ichthyology, phytosociology or myrmecology), while a general encyclopedia can be referred to as a compendium of all human knowledge.
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.
An example would be the Compendium of the Catechism of the Catholic Church, a concise 598-question-and-answer book which summarises the teachings of the Catholic Faith and Morals.
The Bible is another example of a compendium—a group of many writings of the prophets and apostles over a period of time, whose books are put together to form the Old Testament and the New Testament.
Some well known literary figures have written their own compendium. An example would be Alexandre Dumas, author of The Three Musketeers, and an enthusiastic gourmand. His compendium on food titled From Absinthe to Zest serves as an alphabet for food lovers.
The bestiary, popular in the Middle Ages, is another example of a compendium. Bestiaries cataloged animals and facts about natural history and were particularly popular in England and France around the 12th century.