In my view roasting and baking are similar, both done in an oven that's been evenly heated to a temperature. The difference is probably that baking is generally done at lower temperatures and binding ingredients can be part of what's baked (cakes, quiches, etc.) Roasting generally involves meats and vegetables. Grilling and broiling are similar as well, both cook food quickly with high heat. In grilling the heat source comes from the bottom and in broiling from the top. Grilling temperatures can be modified to lower temps, while broiling is always a high heat.