Fog of war
The fog of war in Dark Forest is the portion of the map that is not visible to a player.
Upon creating a new Dark Forest account, only a small portion (the starting area) of the map is revealed to a player and the rest of the universe is covered by the fog of war. Over time, the map is revealed by CPU mining, the speed of which is dependent on the power of the CPU.
"Fog of war" is a callback to various video games like Age of Empires or Starcraft, where a player had vision of certain parts of a game map but not others and more map could be revealed via exploration.
The fog of war in Dark Forest is important to note because it utilizes ZkSnarks. Where the fog of war in a typical video game is more of a shallow veil (the players might not see within the fog of war, but the game servers and the NPCs likely know), Dark Forest has utilized zksnarks so no player nor computer knows what is under the fog of war until it is revealed via the intended means.