Tusing is a term that originated on the r/lgballt discord server. It is defined as when you do not feel like a gender quite fits you, but it is the closest you can find, and you wish to identify with it. 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 fell 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.
Tus originated 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 are in Tucson, when they are not within city limits.