Ket

A ket is Dirac’s notation for a quantum state, written as a vertical bar, a label, and a right-hand angle bracket. The ket labelled 0 is the state certain to read 0, and the ket labelled 1 is the state certain to read 1.

The same brackets take a plus or a minus as the label, and both still fit on the label of a floppy disk. The |+⟩ state has equal amplitudes with the same sign, and the |−⟩ state has equal amplitudes with opposite signs.