Iceberg principle
Also said as Theory of omission, Iceberg theory
Know far more about your world than you show. Hemingway's version: an iceberg moves with dignity because only one-eighth of it is above water, and the rest can be felt.
What is left out does work, as long as someone knows what it is. Hemingway's own warning was that leaving out what you never knew only makes hollow places.
Say it
“Apply the iceberg principle here: write all twelve facts about the siege in the bible, and let the player see only the one on the sword: "Its owner never came back to collect it."”
Where you’ve seen it
A Dark Souls item description might give a few sentences about a knight, naming a lord and a betrayal it never explains. Enough other items agree with it that you can tell the rest of it exists.
Not to be confused with vagueness
Vagueness means there was nothing behind the line. The iceberg means a specific thing is behind it, and that is why the line can be so short and so sure of itself.