Available for a variety of purposes, unsecured loans are personal loans where you don't have to provide the lender with any security, or collateral. That makes them different to secured loans, which are personal loans where you do need to provide security, such as property or a car.
If you default on a secured loan, the lender can seize your collateral, sell it and then use the sale proceeds to repay the loan. If you default on an unsecured loan, the lender will be unable to automatically seize one of your assets.
Don't assume, though, that defaulting on an unsecured personal loan doesn't have consequences or that your debt will magically disappears. The lender might pursue legal action and the court might then order the forced sale of one of your assets. You might also be forced into bankruptcy.