unofficial

An unofficial thing or person isn't officially recognized or accepted as part of an organization or activity.

You'll often hear people talking about unofficial rules at school or university. These are guidelines that aren't written down anywhere, but everyone knows they're there. For example, maybe a group of friends has a tradition to meet up on Fridays, but it's not something the school administrators know about or officially support. In this case, the rule is unofficial because it wasn't made by an official authority and isn't really connected to any school activity.

If you think about it, unofficial can mean two different things depending on the context. If we're talking about a sports tournament, for instance, some teams might be considered unofficial competitors if they don't meet all of the official criteria to participate. But in this case, being an unofficial team doesn't necessarily mean they're not good or that their results won't count – it just means the organizers can't officially recognize them as part of the competition.