ERC-20

ERC-20 is the interface standard every fungible token on Ethereum implements — a handful of functions (balanceOf, transfer, approve, transferFrom) and two events (Transfer, Approval). Because everyone agrees on this shape, a single wallet, DEX, or block explorer can support every ERC-20 token ever created without custom code. The non-obvious quirk worth knowing is the approve + transferFrom pattern: you don't send tokens to a contract directly, you first authorise it to pull them, then call a function on the contract that pulls. This is how Uniswap swaps work, and it's the reason malicious "unlimited approval" calls can drain wallets long after you forget you signed them. USDC, USDT, UNI, AAVE — nearly every token you interact with is ERC-20. NFTs use separate standards (ERC-721, ERC-1155) because uniqueness needs different semantics.