In its comprehensive description of what constitutes privacy, the court said it was about an individual's freedom to make personal choices in life.
The right to privacy, the judges said, "safeguards individual autonomy and recognises the ability of the individual to control vital aspects of his or her life. Personal choices governing a way of life are intrinsic to privacy."
These choices, the court indicated, can even involve death. "An individual's right to refuse life-prolonging medical treatment or terminate his life is another freedom which fall within the zone of the right of privacy," the court said. "'Life' within the meaning of Article 21 is not confined to the integrity of the physical body. The right comprehends one's being in its fullest sense."
Passive euthanasia - ending of life by withdrawing life support to patients who are brain dead -- was made legal in India in 2011. But today's judgment took the issue forward.
The debate on euthanasia had raged across the country in 2011 during the hearing of a petition on behalf of Aruna Shanbaug, a nurse at a Mumbai hospital who had been left in a vegetative state after being raped in 1973. The top court at the time had allowed passive euthanasia, and had left the larger question to a Constitution Bench. Aruna Shanbaug died four years later, in May 2015.
Euthanesia and assisted suicide are acceptable in 10 nations across the world, including US, Canada, Germany, Switzerland and Belgium. Assisted suicide is when the patient decides to end life and is assisted by a doctor. In Euthanesia, the call is taken by the patient's family and friends.
Privacy, the judges today said, includes at its "core" the "preservation of personal intimacies, the sanctity of family life, marriage, procreation, the home and sexual orientation" - words the gay and LGBT community said gave them hope.