In Webster's Collegiate Dictionary, bake and roast are both defined as cooking by exposure to dry heat, as in an oven. They are usually not used interchangeably, however. Usage is sometimes quite idiomatic. Pe, every native English speaker knows what a baked potato is, but "roasted potato" is not always immediately understood (as the entry by SrRdRaCinG makes clear).Definition for roast/bake (from WR Dicitonary):
cook with dry heat, usually in an oven; "roast the turkey"
cook and make edible by putting in a hot oven; "bake the potatoes"