Hi Cali,
Salt cod is dried cod fish. When it's reconstituted it has a chewier texture than fresh fish and the flavor is mild. My Grandmother used to buy it at the Public Market here and we (Italian) call it Baccala. When purchased now, other types of whitefish may be used to make it and still be labeled salt cod. If you can't find it in your local grocery store, check local delis and ethic groceries - there are also online sources.
When my Grandmother bought it, it looked like this (the woman in this photo is not me or my Grandmother):

but now you can also buy it packaged:
Salt Cod (Sold by the Pound)Happy Cooking!
Betsy