APR (Annual Percentage Rate) refers to the annualized interest rate that individuals can earn or pay when participating in decentralized finance (DeFi) platforms or lending protocols. It represents the potential return or cost on assets that are lent, staked, or borrowed within the cryptocurrency ecosystem. Users can earn APR by providing liquidity, staking their tokens, or participating in yield farming, while borrowers might incur APR when taking out loans or utilizing certain DeFi services. It's a key metric for understanding potential gains or costs in various crypto financial activities.