From The Dim Future Wiki

The deck is the group of cards that a player uses during the game. It is made of of 3 parts:

  1. The leader
  2. 6 areas: 2 Wastelands and 4 other areas that share a faction with the leader
  3. A group of exactly 50 cards that may not include areas or leaders. This is the group that is drawn from.

In addition, the deck may not include more than 4 cards with any given name.

Often, the word "deck" is used to refer to the 50 cards that are drawn from during the game. This meaning of "deck" is a zone of play during the game.