Both ERC-721 and ERC-1155 are standards for NFT tokens. ERC-721 only allows creators to mint a single NFT and create a smart contract for each new NFT. ERC-1155 is an improved version of ERC-721, and it allows creators to mint multiple NFTs (as well as fungible tokens) with one smart contract. It is like a vending machine for NFTs, where a single contract can be used to mint unlimited NFTs.