What is Section 377, the 1862 law that criminalises homosexuality?

Section 377 of the Indian Penal Code (IPC), which came into force in 1862, states, "Whoever voluntarily has carnal inter­course against the order of nature with any man, woman or animal, shall be punished". Under the section, consensual sexual acts of adults such as oral and anal sex in private between heterosexuals are also considered "unnatural" and are punishable.