As far as I know, a vocal range is the range within which you can comfortably sing. c:
If you keep deepening your notes while singing, you'll eventually get to a point where the notes will become distorted and airy, and you can't hit them anymore. Same thing when you sing higher and higher, eventually your voice will get crack, thinner or perhaps even stop.
This is a vocal range chart I found on Wikipedia:
I myself am likely a Soprano, seeing as my absolute deepest is around F3, and highest about C6. One's vocal range changes depending on how much you train it and how. When I was a kid, I remember I had trouble singing anything below C4. xD
My friend (female) however, has an amazing deep range. It's difficult to say what she'd be, as last time she checked her highest was ~A5, and lowest around C2.
What do you believe your range is? :3