Barbecue is a method and apparatus for cooking food (generally meat). In the United States, to grill is to cook meat relatively quickly using the direct heat imparted by a charcoal or propane fire, while barbecue is a much slower method utilizing the indirect heat imparted by the smoke of a wood-fueled fire (and tended to over an extended period of several hours).
While there is a vast degree of variation and overlap in terminology and method surrounding this form of cooking, the generally accepted difference between barbecue and grilling is in the cooking time and the type of heat used: grilling is generally done "hot and fast" over direct heat from low-smoke fuels (with the flame contacting the meat itself), while barbecuing is usually done "low and slow" over indirect heat from high-smoke fuels (with the flame not contacting the meat directly).
The term as a noun can refer to the meat or to the cooking apparatus itself (the "barbecue grill" or simply "barbecue"). The term as an adjective can refer to foods cooked by this method. The term is also used as a verb for the act of cooking food in this manner. Barbecue is usually done in an outdoor environment by cooking and smoking the meat over wood or charcoal. Restaurant barbecue may be cooked in large brick or metal ovens specially designed for that purpose. Barbecue has numerous regional variations in many parts of the world.