Deck

From Memory Alpha, the free Star Trek reference.

A Deck refers to one of several levels of a starship or similar vessel.

On Federation starships, the upper level is usually referred to as deck 1. Deck numbers increase for each deck below, the lowest level has the highest number (for example, the Galaxy-class USS Enterprise-D's lowest deck was deck 42.

It is possible for a ship to have a series of internal sub-decks or split levels that are numbered differently.

The refit Constitution-class USS Enterprise-A had an internal turboshaft system that had deck numbers that ranged from low numbers at the bottom of the shaft, to deck 78 at the top. This was in contrast to the fact that the Enterprise was at the time 23 decks high, with the bridge on deck 1. (Star Trek V: The Final Frontier)
- Director William Shatner decided that it would be dramatically necessary to have the deck numbers increase to give the illusion of height. Its possible the shaft was on a different up-down axis as the rest of the ship and the heroes were actually moving lower or sideways (but with gravity beneath them), another possibility is that the deck numbers increase back upward along the shaft to correspond to split-level arrangements in the hull we don't know about.
The Defiant-class of starship is four decks in height, but have been referred to as having a deck 5 and deck 6 somewhere in their structure.
- The dialog establishing the existence of decks 5 and 6 conflicts with graphics showing only four on the ship, however, they may be referring to control areas in the lower nacelle booms, that wouldn't appear on a centerline graphic.
The Sovereign-class USS Enterprise-E was 24 decks in height, but had secondary hull sub-decks or some split-level arrangement that allowed for more than 29 deck numbers. (Star Trek Nemesis)
- William Riker dropped the Reman enemy (unnamed Remans) from deck 29, and he dropped several more levels. Its possible they were on a different gravity plane, and he was actually dropping sideways or up into the ship's machinery, hence the extra deck numbers, or that decknumbers again moved upwards back up into some internal structure.