The raisin is the dried fruit of any old white grape and includes sultanas.
The sultana is the dried white, seedless grape of Turkish, Greek or Iranian origin, from a grape variety of the same name. These are typically larger than the currants made from Zante grapes, but smaller than "normal" raisins Sultanas. In the US sultanas are almost all made from Thompson Seedless white grapes, and result in a sweet, concentrated dried fruit. They may also be made from Muscatel grapes.