noun A column vector, in Hilbert space, especially as representing the state of a quantum mechanical system; the complex conjugate transpose of a bra (a row vector); a ket vector. Symbolised by |...〉.
A particular ket, say |A⟩, might be represented by a particular column vector. Its corresponding bra, ⟨A|, would then be represented by the row vector which is the transpose conjugate of that column vector.