AU

From Hpwiki

AU is the term used for fanfics (or other) dealing with Alternative Universes of a known canon story. Generally, anything that deliberately contradicts canon can be termed AU.

The most popular AU scenarios in Harry Potter fanfics deal with Harry growing up with his parents or Sirius Black, someone else being the prophesied hero, and/or Harry being sorted into a different house (typically Slytherin). Another branch of AU stories are those where some canon character is transported into another universe where everything is completely different. A special cases are crossovers, wherein characters, places or "rules" of different canon "worlds" meet or are combined.

Note that stories that are true to canon do not become AU as soon as new information is revealed. Rather, they keep close to canon as it was known when the story was written.