lower decks

/L OW1 ER0 D EH0 K S/
noun
  1. 1

    The deck of a ship immediately above the hold

  2. 2

    (by extension) Those members of a ship's company who are not officers.

Source: https://en.wiktionary.org/wiki/lower%20deck, https://en.wiktionary.org/wiki/lower%20decks