I can’t be the only one who wondered about this.
A .doc, .docx, .rtf, .txt file might contain what we call a document. A .png or .jpg file contains a picture. A .zip, .tar.gz, .rar file contains an archive.
What the heck do .qb files contain?
“Object” is kind of vague. Everything after that is unwieldy: “voxel object”? “voxel shape”? “3D asset”?
Is there a secret word all the pros know that I’m missing?
well, clearly .qb is the filetype extension for qubicle constructor (as well as, apparently, quickbooks … 
) and contains (I would imagine) the necessary details for reconstructing a 3D shape within Qubicle Constructor…
as such, I think your last suggestion for 3D asset makes the most sense… 
Qubes, clearly!!!
Qubes, clearly!!!
Hmmmm… I don’t hate this…
I don’t know the details behind it, only what I’ve heard from other posts (here’s one!)
@RepeatPan pretty much says that it’s just a bunch of RGBA values, I haven’t experimented with those files myself though so I can’t tell you any more than that. 
Qubicle Binary. As has been said before, really abstract it’s a bunch of colors. A little less abstract it’s a bunch of colors arranged in a 3D space. A little less abstract it’s a bunch of colors arranged in groups in a 3D space.