It's really not that hard to define a mini velo. It's a bike with road or hybrid geometry that happens to have 20" or smaller wheels.

Yes, there are variations on this. You can probably find examples of all kinds of bikes with small wheels (I do recall seeing a small wheeled mountain bike), and you can call them all mini velos if you like. However, that one sentence description should fit most mini velos on the market right now... and will probably fit most of the ones produced by BD.

--sam