Definition courtesy of Merriam-Webster:
In the Middle Ages, it was customary for men to wear cloaks with hoods indicating their professions.
Doctors wore one style, clergymen another, artists and musicians yet another.
In associating hood style with profession, most anyone could tell at a glance what business a man was in.
The downside to this system, of course, is that someone could pass themselves off as part of another trade.
The false hood worn gave meaning to the deception attempted.