NRE vs NRO account
An NRE account holds money brought into India from abroad and can be sent back out freely; an NRO account holds income earned inside India, is taxed there, and can only be sent back out within limits.
NRI — Non-Resident Indian — describes a person. NRE and NRO describe two kinds of account that person can hold, and the difference between them is not cosmetic.
An NRE (Non-Resident External) account is funded from outside India. Its balance and its interest are freely repatriable, meaning the money can be sent back out of the country, and the interest is not taxed in India.
An NRO (Non-Resident Ordinary) account is for income arising inside India — rent, dividends, a pension. Interest is taxed in India, tax is deducted at source, and repatriation out of the country is subject to annual limits and paperwork.
Which account a transfer should be paid into is the recipient's decision, and it depends on what the money is. We ask rather than assume, because the choice affects what they can later do with it.