When people, with the benefit of years (or generations) of hindsight and typically with ulterior motive, try to rewrite history as it originally occurred.
1) "The Holocaust was media sensationalism. Assuming it even happened, it was exaggerated and is revisionist history.
2) "Alabama was National Champions of College in 1941, per the Houlgate Poll. And became revisionist history in 1983 thanks to UA SID Wayne Atcheson, who'd go on to be author a fantastic biography about Jay Barker." citation needed