1. Mother Tongue - This is the first language taught by the parents and spoken since childhood in the household. In other words, the first language a person speaks from when they are taught how to speak and is spoken in the household is the mother tongue. When recording the mother tongue of newly born infants, the language spoken in the household should be written. Different languages are spoken in various places of Nepal. The first language that anyone speaks in the household since childhood should be written as the mother tongue. If the person is unable to speak, then indicate mother tongue as "Sign Language". There can be members speaking different mother tongues in one household. So, mother tongue of head of the household and other members of the household could be different.

Mother tongue can be different according to the caste/ethnic group. A person from same caste/ethnic group can have different mother tongue due to difference in social, cultural, geographical situation. For example, a person of Magar caste might not know Magar language. Children born from the parents with different caste/ethnic group might have different mother tongue than that of their parents.

In the course of enumeration, the meaning of mother tongue should be made clear to the respondent, and the mother tongue of every individual in the household should be asked and written. Examples of the mother tongue are as follows: Nepali, Maithili, Bhojpuri, Magar, Thakali, Tamang, Limbu, Awadhi, etc.