377. Unnatural offences.

Whoever voluntarily has carnal intercourse against the order of nature with any man, woman or animal, shall be punished with imprisonment for life, or with imprisonment of either description for a term which may extend to ten years, and shall also be liable to fine.

Explanation-
Penetration is sufficient to constitute the carnal intercourse necessary to the offence described in this section.

CLASSIFICATION OF OFFENCE
Punishment—Imprisonment for life, or imprisonment for 10 years and fine— Cognizable—Non-Bailable—Triable by Magistrate of the first class—Non-compoundable.

You should read this short article on Section 377 that talks about recent decision by the Supreme Court on homosexuality in India (2 minute read)