What's a "MicroCar"?
A special, loveable, small sort of car!
Beyond that, opinions vary! There’s no formal definition, but nowadays we usually take it that a microcar should have no more than 3 cylinders, be under 700cc, and be designed for economy motoring. Or something like that ...

A 2004 Smart Roadster
Smart Roadster By Brian Snelson / CC By 2.0
Microcars have been around throughout motoring history. More than a motorbike, but somehow not quite a "full" car, early models were called "cyclecars".

The 1919 Busy Bee, a home-made cyclecar.
They reached their heyday, in Britain and Europe, after the Second World War, when steel supplies were difficult, lots of people wanted cars but couldn’t afford the usual models, and difficult fuel supplies meant that economy was more important than size and performance.
Some microcars had four wheels, but many were three-wheelers – in the UK, three-wheelers were cheaper to tax, and most could be driven on a motorbike licence. Having only three wheels also makes a car lighter and simplifies the suspension (just as a 3-legged stool doesn’t rock, a 3-wheel car can always have all its wheels touching the ground, without stressing the chassis). It’s also much easier to attach a chain drive to just one wheel!
Keeping the car small, but making the inside big, gave some microcars a rather "pumped up" look. With their clear plastic canopy windows, these became the famous "bubble cars".

A 1959 Isetta 300 bubble car
The NMCR features mainly classic microcars, from before the war through to the 1960s – but microcars are still made. Licensing and tax laws mean that there’s still a market (especially in France and Italy) for these hardworking little vehicles.