A term coined by Dirac in 1947 to describe a vector in a function space that represents a wavefunction's complex conjugate. Kets are the notation for the corresponding vector representing a wavefunction. The words come from splitting "bracket", since when combined, the notation for looks like a bracket. "We shall call the new vectors bra vectors, or simply bras, and denote a general one of them by the symbol < |, the mirror image of the symbol for a ket vector." P. A. M. Dirac in "Principles of Quantum Mechanics"
I've been working on a paper today, and included an equation using bra and ket notation (which I find generally easier to follow than the intergral notation), which is what brought this to mind -- either that or it was the laundry I was folding!
5 hours ago in The Phytophactor