Perfect information

Contrast. (things that deny perfect information)

• Fog of War
  
• Random Elements (**probably)
  
• Simultaneous Turns

... and many others

** Random elements can be tricky and the role of random elements in game theory is not entirely agreed on by scholars. The initial conditions could be randomized in a Perfect information game. As long as both players are shown the result at the same time, Perfect Information is preserved (this is undisputed). Suppose each player is given random attributes at the beginning of the game, most likely causing Asymmetric Factions? This is not a disqualification if each player knows their own and opponents' attributes before play.

Compare Chess with perfect information to Stratego with imperfect.

Note that this does not include knowledge of your opponents plans, although you can deduce such from the information you have as always.