Casual, IMHO, means collared shirt and nice pants for males. Jeans are OK if they are neat & tidy. Women have greater latitude but NO CLEAVAGE. Either gender should avoid TShirts, sweats, or athletic shoes.
That's my opinion but I think they are general conventions. Part of how you present yourself will also be your acumen at understanding societal norms. Clothes aren't everything and your interview isn't a beauty contest -- but appearance can say a lot and leave impressions, subtle or grand.
clienk: if someone says casual, certainly don't wear a business suit.