Somebody that is completely obsessed with Musicals and lives only for them. Listen to their iPod and it will be completely filled with 'Billy Elliot' , 'Wicked' or 'Les Misérables'.
Mention anything to do with Musicals and they will burst in to song and then continue to sing a medley of all of their favourite songs from their favourite West End Shows.
A typical Musical Geek would say:
Geek 1 : 'Oh my goodness, guess which Wicked song came on earlier?'
Geek 2 : 'I'm limited. Just look at me - I'm limited?'
Geek 1 : 'And just look at you, you can do all that I couldn't do, Glinda'
*Excited squeals*