What is it?
Supply APY is the current annualized rate suppliers are earning, expressed as a percent. It is a snapshot of today's rate, not a guarantee for the next year.
Why does it matter?
It tells you what the pool is paying right now. It moves with utilization and with Aave's rate strategy. A sudden spike often means the asset got busy.
Example
USDC supply APY sits at 3% one week and 8% the next after utilization climbs. That is the pool bidding for more supply, not Ronnie forecasting 8% forever.
Where can I find it?
Markets (USD-weighted supply APY for the whole market). Assets and asset detail (per reserve). Cross-Chain compares supply APY by chain.