Grill - To cook food over high heat, often over a flame or coals. Food prepared this way has black lines known as Grill marks such as steak, hamburgers and, chicken. Roast - To cook in an oven, generally we roast meats and bake bread even though the cooking method is the same. Barbeque - To cook food over wood coals, generally slow cooking method done outdoors. Can also be a flavor as in barbeque sauce.

Through images: https://goo.gl/ZPRnEi Through definitions: http://www.thefreedictionary.com/grill