What is Section 377 of Indian Penal Code?

Section 377 of IPC states: 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 offense described in this section.

The law violates Article 14 of the Constitution, which guarantees all people "equality before the law;" Article 15, which prohibits discrimination "on grounds of religion, race, caste, sex or place of birth;" and Article 21, which guarantees "protection of life and personal liberty."