Information hiding
Also said as Hidden information, Withheld stats
Deliberately leaving out a number the game knows, so the player has to read it from the world or work it out. In other words, deciding what the HUD should keep in the fog.
Everything you show becomes what people look at. Show the boss's health and they watch a bar; hide it and they watch the boss. Hide something the player can't work out any other way, though, and it just feels unfair.
Say it
“Don't show the boss's health. Give it three visible stages instead: cracks at 60%, a slower walk at 40%, a limp under 25%.”
Where you’ve seen it
Monster Hunter shows no health bar for its monsters. You learn to read them: they limp, they tire and drool, their parts break. The trap in this toy works the same way as the game's, which only captures a monster that is badly hurt.
Not to be confused with fog of war
Fog of war hides parts of the map until you scout them. Information hiding is about stats and states, like the health of the thing right in front of you.