Tusing is the act of identifying something that doesn't quite fit you, but is the closest idea that you can find. For example, if you do not feel like you are fully asexual, but you are sex repulsed and feel more comfortable identifying as ace, you can say you are tusing asexual. Another example would be if you feel that you are in between cis and gender fluid, you could say you are tusing cis and gender fluid. Any LGBT+ or MOGAI identity can be tused.
The word tus was first used on the r/LGBallT discord server. It comes from the airport code for Tucson, Arizona, after a discussion about how identities are not always exactly perfect fits, and sometimes the line around identities is weird. This was compared to how addresses in Arizona say that they are in Tucson, despite not being within city limits.