What does B stand for in a school bus?

What does the "B" in school bus actually mean? Ugh, school buses. Just thinking about them brings back a flood of memories, mostly involving the smell of old vinyl and the terrifying screech of brakes. So, the "B" in Type B school bus... it's all about the build, apparently. Meaning, it's got this super-stripped-down chassis, you know? The door's behind the front wheels – practical, I guess, but not exactly glamorous. They even get all technical and split them into B-I and B-II based on weight. B-II being the heavier one, right? I think? I mean honestly, who remembers that stuff? GVWR? Give me a break! It's like, who cares about the Gross Vehicle Weight Rating? It's just a bunch of numbers, a boring bureaucratic label. I remember mine, though – it was bright yellow, smelled like diesel fumes, and always seemed to be on the verge of falling apart. It even had this weird dent on the side, I think from some kid kicking it or something, I can still see it so clearly in my mind. And that noise – oh god, that awful rumbling noise it made, it was so loud! It was always slightly terrifying, especially on rainy days, which was often the case in my town. So yeah, "B" for basic, boring, and a little bit frightening, that's my take anyway.