Satī, often spelled and pronounced "suttee," is a banned funeral practice of Indian cultures. The practice consisted of a widow voluntarily burning herself alive on her dead husband's funeral pyre; the practice was commonplace throughout India, and was regulated by British regimes which required the widow to be of sound mind and the ritual performed according to strict custom, not at random. However, it was banned by various governments and regimes several times, and is not currently practiced legally. The 1987 Prevention of Satī act was intended to eliminate the practice entirely, but examples still occur, sometimes without the consent of the widow. In the novel, the burning of a woman is interrupted by Phileas Fogg, who sees the practice as barbaric, and it is clear that Verne's idea of "civilized" culture abhored the concept entirely:
"Yes," returned Sir Francis, "burned alive. And, if she were not, you cannot conceive what treatment she would be obliged to submit to from her relatives. They would shave off her hair, feed her on a scanty allowance of rice, treat her with contempt; she would be looked upon as an unclean creature, and would die in some corner, like a scurvy dog."
(Verne, Around the World in Eighty Days, gutenberg.org)
This description is not entirely accurate, but understanding of Indian culture was not well-advanced in those days. In any case, the ritual is stopped and the woman saved; she acts mostly as a passive love-interest for Fogg and has little effect on the plot, serving mostly as a British condemnation of "primitive" religious ritual.
The custom of Suttee involves the destruction of a widow following her husband’s death. It is an old Hindu custom. The widow was burned to death. The widow’s age is irrelevant. Some believe the custom evolves around the story of the goddess Sati. She was grieving for her deceased husband. Feeling overwhelmed by her grief she threw herself upon the fire of his pyre. It became illegal in India in 1892. However, some believe that the practice may still occur in some societies of India.
India has a longstanding history of tribal conflicts. Many men died during the conflicts leaving behind widows. Rather than be at the mercy of soldiers who might rape or harm them in other ways, some women took it upon their own initiative to end their own lives following the death of their husband. In some instances this ceremony changed to become a mandatory response to a husband’s death leaving no choice for the grieving widow.