A music zombie is someone who spends 95 percent of their waking hours thinking about, listening to, playing or performing, teaching, or talking about music.
A zombie is a fictional (you mean they aren't real!?) undead person in an entranced state. In pop culture they are usually found mindlessly searching for one thing and will be stopped by nothing in the pursuit of that thing. In the case of a zombie that thing is, commonly, braaaaaaaiiiiins!
In the case of a music zombie, it is all things music. This includes, but is not limited to: pop music, opera, classical, musical theatre, jazz (all forms), rock and roll, world, hip-hop, rap, and country (and western!).
A music zombie is interested in how musical instruments work and where they came from. The zombie wants to know how to play the instruments and maybe even how to repair them.
A drive in the car becomes an internal essay about how a specific song on the radio is being performed, thought is given about an unusual back-story, or a form or structure is being analyzed (the zombie in the car is also prone to singing along with the CD or radio. Loudly.)
A walk in a mall becomes a distraction when an interesting song comes up in the background. It becomes a particular distraction when the zombie's favourite band comes on and the zombie can't leave the store until the song is over.
The zombie can no longer read with music in the background because the zombie's braaaaaaiiin is instantly pulled away from the book.
Maybe you're a music zombie too.
*GASP!* LOOK OUT!! THERE'S ONE BEHIND YOU! AND IT'S GOT A CLARINET!