noun: (medicine, countable) A behind the ear hearing aid.
adjective: (medicine) Initialism of behind the ear. [(medicine) Describing a type of hearing aid with microphone, amplifier, and battery that sit in a unit behind the wearer's auricle, and the amplified sound is passed down a tube into the ear canal.]
noun: (physics, uncountable) Initialism of Boltzmann transport equation.
