Usury means the practice of collecting interest on money lent, in order to receive more than was lent. That is always wrong, because money is meant to be spent, it has no other use.
However, no one would ever loan money if they could not have the principal returned. So if a currency is known to be depreciating, some level of interest would be necessary to ensure the return of the principal.
And if someone provides money for something like a house or some other income generating property for someone else, then they could have just reason to desire to share in the profits they would otherwise have made until they are repaid the principal of their loan.