Lending Protocols are a genre of decentralized apps that are built around the concept of building a decentralized debt marketplace. A lending protocol is composed by: Suppliers/Lenders: The people who back loans within the debt marketplace in some capacity. Borrowers: These are the people who take on the debt and enable suppliers to earn a return on their funds.
In order to get a loan, the borrowers must deposit enough credit, more than the amount borrowed, with the lending protocol setting a collateralization ratio that borrows must be maintained, If the asset you deposited lose enough value to then be less than the amount borrowed, the deposited asset will be liquidated and used to pay the loan back with an additional penalty fee. In order to do this and track different assets prices, the smart contract of the lending protocol must have a source of data that tells them the price of every asset that can be supplied and borrowed, that task is performed by an oracle! So in theory The Currency Index may be used in a similar way to lend or borrow The Currency.