Peer to peer lending (or P2P lending) is where you are matched with borrowers who would like to take out a secured or unsecured loan.
You deposit your money just like a savings account. Your provider will then lend your deposits to an individual or business as normal, with an agreement that the funds will need to be repaid with additional interest on top.
It includes a small amount of risk, but you can often get a much better interest rate compared to a standard savings account.