Culture Bomb is a special effect in Civilization VI which instantly expands a civilization's territory into nearby neutral, or even foreign-owned territory. Culture bombing is the only way of taking non-neutral territory in the game, barring military conquest or diplomatic negotiations involving switching cities.
The Culture Bomb is triggered on a specific tile (usually by building a tile improvement or district). The result is the immediate annexation of all surrounding tiles without districts or wonders and falling within 3 tiles of one of the owner's City Centers. Tiles in which wonders or districts are being constructed are still flipped under the effect of a Culture Bomb, wiping out any unfinished construction in the process.
A Culture Bomb may be triggered by a number of special sources within the game. Typically it is the case of civilization-specific abilities, such as Poland's ability Golden Liberty (the requirement being constructing Encampments or Forts), Australia's ability Land Down Under (where building Pastures triggers the bomb), the Dutch ability Grote Rivieren (where it's triggered by building Harbors), the Māori civilization's ability Mana (after building Fishing Boats) or Jayavarman VII's leader ability Monasteries of the King (where it is triggered by finishing Holy Sites).
Nonspecific Culture Bombs can be unlocked via other means. Notably, the Enhancer Belief Burial Grounds lets any civilization Culture Bomb by completing a Holy Site, and the Great Engineer Mimar Sinan grants it (with Rise and Fall) when completing an Industrial Zone. The World Congress resolution Border Control Treaty will trigger a Culture Bomb upon the completion of any district to whoever wins it.