1. Secondary, subordinate, or supplementary item accompanying a primary item. 
2. Specific asset (such as land or building) pledged as a secondary (and subordinate) security by aborrower or guarantor. The principal security is usually the borrower's personal guaranty, or the cash flow of a business. Except for highly creditworthy customers (who can get loans against only their signatures) ... Read more

USAGE EXAMPLE

When letting Sarah borrow my camera, I wanted her to give me her laptop as collateral in case she lost or damaged it.