A bus is a heavy-duty commercial passenger vehicle built on a truck-style chassis with air brakes and heavy suspension. In automotive shop slang, bus is also a derogatory nickname for a large, poorly handling, or incredibly slow passenger car, particularly an oversized SUV or a full-size van that feels ponderous to drive.
Heard on the job
I hate test-driving that customer's Suburban, it steers like a bus and takes up two bays.