A probability-based guess about hidden facts in the current situation.
Belief state is like playing Clue with half the cards hidden. Your suspect list changes after each clue.
Robots and game AIs use it to decide with missing facts. New clues change the guess.
MDP
Belief state often replaces the direct state if the world is partly hidden.
World model
Belief state can be the World model’s current guess about the scene.
Stateful agent
A Stateful agent keeps and updates this guess as things change.
Memory
Memory stores what happened before. Belief state turns it into the current guess.