What is "bug's"

Busan-Ulsan-Gyeongsangnamdo is a South Korean metropolitan region encompassing the metropolitan cities of Busan and Ulsan, together with the province of Gyeongsangnamdo. Until 1963 the whole area formed the province of Gyeongsangnam-do. The entire region has a population (as of 2014) of 8,202,239 over an area of 12,424 km². It is Korea's second most populated urban region after the Seoul Capital Area, containing approximately 17% of Korea's population. The GDP in this area is $283.6 billion, a match with Taipei and Atlanta. Brookings Institution reported that BUG's is the 32th ranking city of the world's leading global cities.