Collateral is an asset a borrower pledges to a lender as security for a loan or other financial obligation. It gives the lender a claim on that asset if the borrower fails to repay on the agreed terms.
Collateral can be real estate, vehicles, cash, investments, inventory, equipment, or accounts receivable. The asset usually has to be worth enough to support the loan, though a lender may value it below its market price to allow for the cost and risk of a sale after a default.
Collateral is what separates a secured loan from an unsecured loan. A secured loan is backed by a pledged asset the lender can seize; an unsecured loan has no such backing, so the lender relies on the borrower's creditworthiness and usually charges a higher rate.
You take out a USD 300,000 mortgage to buy a house. The house is the collateral for the loan.
If you repay the mortgage on the agreed terms, you keep ownership of the property. If you default, the lender can foreclose on the house and sell it to recover the unpaid balance.