The Latin term ab initio means from the beginning and is used in several contexts:

• when describing literature: told from the beginning as opposed to in medias res (meaning starting in the middle of the story). See also: List of Latin phrases

• as a legal term: See List of legal terms

• in sciences (especially physics and chemistry): from first principles. A calculation is said to be "ab initio" (or "from first principles") if it relies on basic and established laws of nature without additional assumptions or special models. Experimental input in ab initio calculations is limited to the determination of values of fundamental physical constants
• in military aviation: The very first stage of flight training, almost always on piston or turboprop aircraft

• as part of some Educational qualifications, for example the International Baccalaureate, foreign languages may be taken ab initio - for beginners.

• in ETL: Ab Initio is a tool used to manipulate data.