Short answers, pulled from the story.
Parinirvana describes the state entered after death by someone who attained nirvana during their lifetime. It implies release from karma and rebirth along with the dissolution of the skandhas, the aggregates that make up a being.
Ordinary death sends a person's unresolved karma into a new birth among the Six Paths of samsara, but a person who has attained nirvana breaks that cycle entirely. When they die, the five aggregates, or skandhas, simply cease to occur instead of reassembling into a new existence, a state called nirvana without remainder, or khandha-parinibbana.
The Mahaparinibbana Sutta, a Theravada text catalogued as Digha Nikaya 16, is resorted to as the principal source of reference in most standard studies of the Buddha's life. It was first committed to writing hundreds of years after the Buddha's death, but scholars value it for its attention to detail.
The Mahayana Mahaparinirvana Sutra, also called the Nirvana Sutra, gives almost none of the historical detail of the day of death, mentioning only the Buddha's illness and Cunda's meal-offering. Instead, it uses the event as a springboard for teachings such as the Tathagata-Garbha or Buddha-Dhatu doctrine, the eternality of the Buddha, and the fate of the Icchantikas, and it describes parinirvana as the realm of the Eternal, Bliss, the Self, and the Pure.
Waddell suggested that Kusinagara, where the Buddha died, may ultimately be found in the region of Rampurva, north of Bettiah and in the line of the Asoka pillars leading from Patna, in the Indian state of Bihar. The site has not undergone proper archaeological excavation to confirm this.
In Buddhist art, the event is represented by a reclining Buddha figure, often surrounded by disciples.