Fully onchain games (FOGs) store all game logic, state, and player interactions on a blockchain, as opposed to 'crypto games' that merely use tokens or NFTs as items in otherwise traditional server-based games. In a FOG, when you move your character, that's a transaction. When damage is calculated, that's smart contract execution. When loot drops, the randomness comes from blockchain-native sources. This creates unprecedented transparency (every game action is publicly verifiable), composability (other developers can build on top of the game's contracts), and permanence (the game exists as long as the chain does). The trade-off is performance: onchain computation is slower and more expensive than traditional servers, requiring creative game design that works within blockchain constraints.