rear axle?

what does that mean? Rear axle is a semi-floating hypoid type.

Maketing words if you ask me :)

so what type of axle is it? open diff? posi? i'm looking into because my 71 mustang has it in it.

A hypoid gear is the type found in a typical differential (ring and pinion). Semi-floating, in simple terms, means the axle shaft is carrying the weight of the vehicle. A full-floating axle does not carry the vehicle weight on the axle shaft (look at a 3/4 or higher ton truck). You have a normal passenger car axle. It could be a posi or open type, you'll have to dig further to find out.