NRO : Non-Resident Ordinary account. It is used to park Rupee based Indian earnings in India. An NRO account can be opened by an NRI in a single name or jointly with a resident.
NRE : Non-Resident External account. It is used to park the overseas earnings remitted to India and converted to Indian Rupees.
The basic difference between the two is that an NRO account is used to park the India based earnings in Rupees whereas the NRE account is used to park the overseas earnings transferred to India.