Payment protection insurance (sometimes called "loan protection or abbreviated as "PPI") covers your loan or debt repayments should you find yourself in circumstances that prevent you from paying them back. The policy would pay out if you were unable to work because of illness or made redundant for example.
Payment protection policies are often sold as part of the deal if you take out a loan, mortgage or credit card but you can also buy a stand-alone policy which has no involvement with the loan, mortgage or credit card covered by the policy.