BBQ is a casual written short form of barbecue. People use it for meat cooked over a fire or on a grill, for the outdoor meal or party where you cook that way, and sometimes for the grill itself. On signs, menus, and messages you will see the three letters; when people speak English they often still say “barbecue,” though saying the letters “B-B-Q” is very common too, especially in Taiwan. It feels informal — fine for a chat or a poster, odd in a stiff report. As a verb, people also write BBQ for the cooking: you BBQ chicken, you BBQ in the park. It is not a different kind of food from barbecue; it is the same word in a playful spelling.