ABI is an interface between two binary program modules at the level of machine code. In the context of web3, ABIs are crucial for interacting with smart contracts, defining how to encode and decode data when calling contract functions. Developers and smart contract auditors frequently use this term. To excel in working with ABIs, one should understand Ethereum's contract ABI specification, be proficient in encoding and decoding ABI data, and be familiar with tools that generate and parse ABIs.