Definition of a Motorcycle

Official definition : a single track vehicle with two wheels and an engine

Let us now define a real Motorcycle :

The engine should be air-cooled and have a maximum of two cylinders : one cylinder for solo ride and two for duo. Very exceptionally three for performance freaks. The longer the stroke than the bore, the better.
The capacity per cylinder should be a minimum of 500 cc, except for non unit-construction machines and certain forgotten and idiosyncratic 2 strokes.
Each cylinder should have its own exhaust and silencer, preferably of the sausage shape or reverse-cone type.
The wheels should be spoked and not of the hideous cast artillery type.
The saddle should be black. Natural leather is acceptable.
The colour of the motorcycle is unimportant provided that it is black. White or gold pin-striping is acceptable. For the more eccentric one can tolerate Midnight Blue, British Racing Green, Metallic Grey, Blood (Indian) Red and even in cases of extreme fantasy, Candy Gold.

Other vehicles
All other substitutes are not Motorcycles: Consumer durables, poofs bikes, girl-traps, idiot/sucker traps, leisure vehicles, fashion objects, ride-to-work bikes or road burners, but not Motorcycles.
Those machines with over-square, liquid-cooled engines are the complete antithesis of the real motorcycle engine.
The gaping air-intakes and rear lamps akin to the poop of a pirate ship may be common currency today but they have nothing to do with the history of the motorcycle. The cast wheels should not have attempted to leave their wheel-barrow origins behind and it is not by dressing them up in garish colours that this can be hidden. The bodywork with all the stoutness of a pat of butter in the sun, are a sore on the image of the motorcycle. The plastic itself is an abomination.

No, truthfully these machines have nothing to do with motorcycling.
Furthermore the owners of such machines often find themselves a few years later at the wheel of an automobile if they haven;t already ended up into one.

Let us add that a vehicle apparently responding to all the criteria on this page but trying to mimic "Motorcycles of other countries" known since the start of the 20th century and plagiarising notably the esthetics and even the sound of their V twin, can never be but a pale, cut-price imitation. This together with their fadish appearance and very approximate design, not forgetting their disastrous resale value.
This definition of a real Motorcycle has been executed in good faith. :-)
It doesn't of course extend to machines other than touring motorcycles because competition machines have needs that allow any tricks and wizardry in the quest for ultimate performance. Even going as far as inventing 30 years ago the RC 164 with 6 cylinders of 42cc each and musically divine!

Translation by Christopher Paul Geddes