* Tortoiseshell cats have a coat of black and orange/red fur.
* Calico cats have a coat of black, orange/red, and white fur.
So, all calico cats are tortoiseshell, but not all tortoiseshell cats are calico.
Think of it this way:
* Tortoiseshell is like the basic color scheme.
* Calico adds the extra color of white.
Both types of cats are usually female due to the way the X chromosome determines fur color.