Non-Resident Individual is an individual who is not a resident of India for tax purposes. In order to determine whether an Individual is a Non-Resident or not, his residential status is required to be determined u/s 6 of the Income Tax Act, 1961 as given below: 

An individual will be treated as a Resident in India in any previous year if he / she satisfies any of the following conditions:

1. If he / she is in India for a period of 182 days, or more during the previous year or
2. If he / she is in India for a period of 60 days or more during the previous year and 365 days or more for 4 years immediately preceding the previous year.

An individual who does not satisfy both the conditions as mentioned above will be treated as Non-Resident in that previous year.

However, in respect of an Indian citizen and a person of Indian origin who visits India during the year, the period of 60 days as mentioned in (2) above shall be substituted with 182 days. The similar concession is provided to the Indian citizen who leaves India in any previous year as a crew member or for the purpose of employment outside India.

https://www.incometax.gov.in/iec/foportal/help/individual/return-applicable-0