What is it?
Health Factor compares the value of your collateral after Aave's liquidation thresholds with the value of your debt. No debt means Health Factor does not apply. Aave can liquidate when Health Factor is below 1.
Why does it matter?
It is the single number that answers: how close is this wallet to being forcibly repaid? Everything else (prices, LTV, thresholds) feeds this.
Example
A wallet with Health Factor 2.4 has a wide cushion. The same wallet at 1.12 is in Ronnie's Risky band. At 0.99 it is already eligible for liquidation under Aave's rule.
Where can I find it?
Wallets and My position. Ronnie labels Healthy at 2 or above, Watch from 1.5, Risky from 1.15, and Critical below 1.15. Those labels are Ronnie's reading of Aave's Health Factor, not official Aave grades, and never a claim that a position is absolutely safe.