As the name implies, an activity bus is a
school bus (aka
cheese bus) used for
extracurricular activities, as opposed to transporting children to and from
school.
In some school districts, there is a fleet of activity buses that operates independently of the regular school bus fleet. These buses are usually fairly similar to regular school buses: they may have additional features such as luggage racks. Whenever a school class goes on a long-distance field trip, they can reserve an activity bus.
In other districts, activity buses are simply regular school buses from the district's pool that are used to take students home from after-school activities, sporting events, or other school-related functions that would cause them to miss a regular school bus.