Non-Resident (External) Rupee (NRE) is a Rupee account using which the funds can be repatriated. It means that the account can be started with funds which can be either transmitted to abroad or from abroad.
Non-Resident Ordinary Rupee (NRO) is a Rupee account which can be initiated with funds which are remitted either from abroad or are generated in the country itself. The striking feature is that the amount in this account is non-repatriable. However, funds in NRO account can be repatriated based on the rules that are being followed at the time of repatriation.