Section 3(1)(c) in The Illegal Migrants (Determination By Tribunals) Act, 1983
(c)"illegal migrant" means a person in respect of whom each of the following conditions is satisfied, namely:--(i)he has entered into India on or after the 25th day of March, 1971,(ii)he is a foreigner,(iii)he has entered into India without being in possession of a valid passport or other travel document or any other lawful authority in that behalf;