This is something I've wondered for a while now. Why do people put an Astrix after trans* when they're writing about transgendered people? What does the * refer to?

This article explains it really well. Basically, it’s equivalent to the difference between calling someone “gay” and calling someone “queer.” One (gay or trans) is a limiting term that applies to only certain identities, while the other (queer or trans*) is a more open-ended umbrella term that more people can comfortably fit into.