Fungible token

Fungible means interchangeable — any unit is identical to any other unit of the same kind. A $10 bill is fungible (your $10 is mine is anyone's), a specific painting is not. In crypto, fungible tokens are the dollar/currency-like ones: 1 USDC = 1 USDC, 1 ETH = 1 ETH, you don't care which "copy" you hold. Technically the contract tracks balances as numbers per address, not individual items — balance[alice] = 1000 rather than a list of tokens #1, #2, #3. On Ethereum the standard interface for this is ERC-20; every stablecoin, governance token, wrapped asset, and utility token is fungible. The opposite is a non-fungible token, where every unit is unique and individually tracked — that's what NFTs are. The ERC-1155 standard sits in between, handling both in one contract.