Giblets are the turkey's neck, heart, gizzard, and liver, which are usually found tucked, like a prize, inside the cavity. Be sure to remove before brining and certainly before roasting. Giblets make a terrific gravy, but I don't include the liver, as it adds a bitter flavor, so save it in the freezer for another use.
In a medium saucepan, combine giblets, stock, and vegetables. Bring to a boil, then lower to a simmer and cook until reduced by half. Strain and discard solids. In a small bowl, whisk together flour and 4 tablespoons hot broth. Then slowly whisk mixture back into the main portion of hot broth and cook about 5 minutes. Season to taste with salt and pepper.