A Contravariant Vector, denoted . The ket is Dual to the Covariant Bra 1-Vector . Taken together, the Bra and ket form an Angle Bracket (bra+ket = bracket) . The ket is commonly encountered in quantum mechanics.
See also Angle Bracket, Bra, Bracket Product, Contravariant Vector, Covariant Vector, Differential k-Form, One-Form