Margin trading on the exchange is essentially trading with borrowed funds instead of your own. When you place a margin order, all of the money you are using is borrowed from other users offering their funds as peer-to-peer loans on the exchange.
The funds in your margin account are used only as collateral for these loans and to settle debts to lenders. Because all the traditional exchanges are centralized, they control their risks and net exposure internally and thus are able set a leverage, i.e. allow you to post margin amount smaller than the amount of funds you are borrowing.
With Nitrogen borrower's collateral is stored in a decentralized manner in an ethereum smart contract, significantly reducing counterparty risk. There amount of loan is always covered in redundancy by the supplied collateral, so there is no leverage as on traditional centralized exchanges.