Clipping of brassiere.
"Hey bra, are we still meeting up later?"
One of the two vectors in the standard notation for describing quantum states in quantum mechanics, the other being the ket.
Alternative form of bro; friend, mate
In plain English: A bra is an undergarment that women and girls wear to support their breasts.
"She forgot her bra at home and had to wear an old t-shirt instead."
Usage: The term bra refers to one half of the pair used to describe quantum state vectors in physics equations. It is commonly paired with a ket vector to form inner products that calculate probabilities or expectation values.
The word "bra" is a shortened form of brassiere, which comes from the French term for an armored sleeve lining used to protect the arm. This original meaning shifted over time to refer to the garment itself, ultimately tracing back to Latin and Greek words for "forearm."