Reimagining stories are competition stories that do not acknowledge the entire Total Drama canon as it existed when the author started writing the story (or predecessor story, in the case of a sequel). Instead, the story is the author's own vision of how a canon season should have played out. The replaced season is usually Season 1 (Total Drama Island) unless the author has written previous reimaginings, in which case later reimaginings will usually follow the canon sequence (TD Action, TD World Tour, etc.)
Reimagining stories normally use all or most of the canon characters. If original characters appear, one of these will usually be a "self insert" character, i.e. an alter ego of the author.