Yakiniku/Korean BBQ via Chef Taro
Yakiniku is a popular dish in Japan, but its origins are in Korean BBQ. Korean immigrants started the original form of yakiniku, known as horumon-yaki, by grilling tripe and large intestine. Later on, they added meats used in Korean bbq and called it 'yakiniku'. The Japanese have added their own flourish to this dish, but "it remains close to its Korean roots (Chef Taro)."
Here are the most common meats grilled in Korean bbq:
Galbi (Thinly Sliced Beef Short Ribs) or 갈비 (Brooklyn Experiments)
Samgyeopsal (Pork Belly) or 삼겹살 (Maangchi)
According to Simon Park of "The Heart of Food", "Samgyeopsal is nothing more than uncured pork belly, sliced thin like bacon but with the rind removed. The name, which translates to “three layered meat”, is a description of the strata of meat and fat that invariably makes up this cut. Typically, it is prepared in the Korean BBQ style i.e. cooked and eaten at the table one piece at a time. Traditionally, the cooked meat is dipped into a salt & pepper dipping sauce prior to consumption."
Bulgogi ("Fire Meat") or 불고기 (Migi's Kitchen)
Bulgogi with more mushrooms and carrots (Anna's Korean Kitchen Diary)
Wikipedia has an excellent overview of Korean bbq and the types of meat grilled.