By definition, Fanfiction is not canon in any way, shape, or form. However, some stories retain their connection to canon but ignores a specific part for the story. Primarily, this also means a story that sticks to the KP canon, such as ignoring Graduation, yet everything else in Canon remains intact.
These fics fit the Broken Canon mold. However, if they do more than simply selectively leave out a specific part of canon but also diverges in other methods, it does not fit the category but is a case of Alternate Universe. Also consider if Crossover applies.