Mezzo Soprano literally means "Half soprano". In other words, a mezzo can go higher than an alto but (usually) not as high as a soprano. Mezzi generally have richer, warmer tones than soprani. Here is the official mezzo soprano thread. If you're a MEZZO and you know it...
In musical theatre a mezzo usually sings around the G below middle C to A two octaves above middle C. Around there, I might be a tad off. I'm a mezzo and I can sing G below middle C to D above high C (not the first C above middle C but the second) which is my workable range, i can sing higher...one really really good days lol :). They do have richer sounds and a majority are belters, but that doesn't mean sopranos can't be belters either.
examples of mezzo roles: Mamma Rose~Gypsy Smitty~ H2$ Rizzo-Grease Tracy-Hairspray Mabel~The Pajama Game