Change War
A Change War was a time war where rampant time travel constantly rewrote even the most basic facts of the conflict — "a beach whose history is washed out completely by a storm only to be washed in again by the next", written in "palimpsest and smoke".
The Homeworld naturally considered such Wars to be permanently ongoing, even if they seemed to be bounded in time from an exterior, linear perspective. Although there was no fixed history to a Change War, certain specific events could become "locked", such as the deaths of specific individuals.
As the Monk taught the Corsair, the Ghost Wars fought against the Malakh Imperium in the Horsehead Nebula were examples of Change Wars. (PROSE: The Bloodletters)
According to one tour operator, the War in Heaven was similar in nature, except that instead of staying static, the War was constantly getting shorter:
As time travel allows both the Gallifreyans and the Enemy to pre-empt each other's actions and to fight each battle over an dover again, the war itself becomes shorter and shorter and its devastating climax creeps closer and closer to the present-day.
This process became complete in the span of time between the tour operator beginning to explain it and them finishing, forcing them to cancel all tours of this era of Gallifreyan history. (PROSE: Gallifrey: A Rough Guide)