What is it?
Debt is what a wallet owes the pool: borrowed tokens plus accrued interest. If a wallet has no debt, liquidation does not apply.
Why does it matter?
Debt is the denominator of Health Factor. Growing debt (from new borrows or from interest) slowly eats the safety margin even if prices stay still.
Example
A wallet borrowed 8,000 USDC last month. Interest has added a little more. The live Borrowed figure on Wallets is the current owed amount, not the original draw.
Where can I find it?
Wallets and My position show Total borrowed. Asset pages show Borrowed for the whole reserve, which is everyone's debt in that asset, not one wallet.