In the United States, the practice of carrying students by bus to a school outside their own neighbourhood, so that schools have children of different races together instead of separated. This is not just 'taking the bus to school' — it names a specific policy from American history. Because neighbourhoods were divided by race, the schools were too, and from the late 1960s into the 1980s courts ordered districts to move students by bus to mix them. It was heavily argued about, and if you meet the word in a news article or a history book, that argument is usually the point. You will see it spelled two ways: busing and bussing. Both are correct; American writing prefers busing. Outside this topic the word is rare, so if you see it, the school-and-race meaning is almost certainly what is meant. In British English there is also 'bussing' for simply moving a group of people by bus, without the race meaning.