In orthography and typography, letter case (or just case) is the distinction between the larger upper case (capital letters, caps, majuscule, upper-case, or uppercase) and smaller lower-case (minuscule, etc.) letters in certain languages. The term originated with the shallow drawers called type cases still used to hold the movable type for letterpress printing.
Questions having the casing tag regards the User Experience of casing.
Reference: Wikipedia - Letter case