Plain meaning
Start with the shortest useful explanation before going deeper.
The annualized interest rate paid by borrowers in a lending protocol, expressed as annual percentage yield with compounding. Borrow APY is determined algorithmically by the interest rate model based on the pool's utilization rate. On Solana lending protocols like Kamino and MarginFi, borrow APY typically ranges from 2-15% for major assets but can spike above 100% during high utilization periods.