Short answers, pulled from the story.
The word purgatory entered English between 1160 and 1180 via Anglo-Norman and Old French. Before this specific term emerged, Latin adjectives like purgatorius described cleansing fire without naming a place.
The Second Council of Lyon in 1274 defined the teaching for the first time stating some saved souls need purification after death. The council stated these souls benefit from prayers offered by the living.
Pope John Paul II clarified in 1999 that the term indicates a condition of existence rather than a physical location. The Catholic Church teaches that all who die in God's grace but remain imperfectly purified undergo a process called Purgatory to achieve holiness necessary for heaven.
Eastern Orthodox churches acknowledge an intermediate state after death before final judgment but reject the term Purgatory and the notion of purification by fire. They believe souls are judged immediately after death entering either light and rest or a direful condition depending on their faith.
Dante Alighieri wrote his poem Purgatorio during the fourteenth century. His work transformed theological concepts into enduring images of fire and suffering through this poem.