Tortishell and calico's are the same thing. Calico is a more comon name for the color gene, though the "irresponsible parent of the human variety world" tends to call them "tortie's"... this bi-polar issue has aslo been commonly noted as a "tortie-tude".
Another bit of info, some people call them "money cats".. but a true money cat is a male calico, extremely rare and actually a genetic defect. At one time people thought they were worth money because of their rarity. If a irresponsible parent of the human variety happens to get one, no, they don't sell it, they'll often "pet it out" to a private home. They can't be shown and can't be breed due to the defect and can have severe health problems often not living beyond birth.
I may not know a lot about life, but when it come's to cats, it's actually scary how much stupid info I've got! lol.