Meaning of lower deck

low'er deck'

Pronunciation: (lō'ur), [key]
— Naut. Naut.
  1. the lowermost deck in a hull having two or three decks.
  2. the deck next above the lowermost, or orlop, deck in a hull having four or more decks.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.