What is it?
Utilization is borrowed divided by supplied. If $800M is borrowed and $1B is supplied, utilization is 80%. The leftover is available liquidity.
Why does it matter?
Aave interest rates usually rise as utilization rises. High utilization also means less spare cash for withdrawals. It is a stress clue, not an automatic 'unsafe' stamp.
Example
USDC utilization moves from 70% to 90%. Borrowing became large relative to supply, or supply left. Borrow APY often jumps. Withdrawals of USDC get harder until cash returns.
Where can I find it?
Overview KPI Utilization (all covered markets together). Markets and Assets columns. Risk Monitor lists reserves at or above 80%. Cross-Chain compares utilization for the same symbol on each chain.