"Velo" means bike so essentially its a mini bike thats built for an adult to ride. Folding bikes could easily fit in this catagory but they are more know as folders. Of course in general when someone is talking about folders its easy to assume they are talking about a bike with small wheels so mini velo is a pretty good term for small wheeled bikes that don't fold and also separate from say a bmx bike as well. With this definition of mini the wheels are 20 inch wheels or less, but the wheels on my mini velo below are a bit bigger than the BMX wheels most people in the US think of as 20 inch. Long story short a mini velo is basically a bike with small wheels that has a frame that is built for an adult to ride it.