A flamen was a priest of the ancient Roman religion who was assigned to one of fifteen deities with official cults during the Roman Republic. The most important of these were the three flamines maiores, who served the important Roman gods Jupiter, Mars, and Quirinus. The remaining twelve were the flamines minores. Two of the minores served deities whose names are now unknown; among the others are deities about whom little is known other than the name. During the Imperial era, the cult of a deified emperor also had a flamen.

The vocabulary of ancient Roman religion was highly specialized. Its study affords important information about the religion, traditions and beliefs of the ancient Romans. This legacy is conspicuous in European cultural history in its influence on later juridical and religious vocabulary in Europe, particularly of the Christian Church. This glossary provides explanations of concepts as they were expressed in Latin pertaining to religious practices and beliefs, with links to articles on major topics such as priesthoods, forms of divination, and rituals.