A "bulkhead" is a solid wall or barrier that separates different areas or compartments within a building or vehicle. It is used to maintain structural integrity, prevent the spread of fire or water, and provide privacy. Full definition
Seat 11 B is a Business Class Bulkhead seat in the upper deck of the aircraft whose close proximity to the lavatory may be bothersome as it is the only one on this deck. (seatguru.com)
I'm always in favor or getting rid of bulkheads because so often, it's not actually serving any purpose, and allows for taller upper cabinets. (soulstyle.ca)
Seat 36 D is a Premium Economy Class Bulkhead seat with restricted legroom. (seatguru.com)