The period in FTM transition where you're taking the right dose of testosterone, but you're not off of hormone blockers yet.
Named so because, supposedly, your voice is just low enough that you can
nail all three parts of the Erlking.
(Some trans men
don't experience the Erlking sweet spot due to
never being on hormone blockers.)
John: Are you still on hormone blockers?
Carlos: Yeah, I'm in the Erlking sweet spot right now.
John: Oh, you should sing the Erlking!