Dinky little motorcycle, usually with an engine below 125 cc. Smaller than a scooter. In some cases it looks like a clumsy bycicle with a motor tacked on. One prime example is the Ciao, but Peugeot has many models as well.
I suspect this to be a British word. Anyway, the mopeds are almost absent in the US, and very present in Europe and Asia. For example, Bamako is positively infested with them.