drop seat

noun
  1. a hinged seat, as in a taxicab or bus, that may be pulled down for use when an additional seat is needed.
  2. a rear panel, as on long one-piece underwear or children's pajamas, that may be opened and lowered separately.

Origin of drop seat

First recorded in 1925–30
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018