What is an electronic cigarette?

What is an electronic cigarette?  Well, in short it is a miniaturized vapourizer, much like a very small, high-tech smoke machine.  It generally consists of (from right to left) a battery, an atomizer, and a cartridge for the e-liquid.

It is not smoke, nor is the person smoking in any sense of the word.  They are vaporizing.

This allows the user to ignore no smoking laws without guilt, as the vapor is also non-staining, and not harmful to others.  It quickly disperses into the air without leaving yellowish gunk, as cigarettes do, instead leaving a very, very faint aroma, as if someone had spilt vanilla extract (or whatever flavour the juice is) a few days ago.

https://en.wikipedia.org/wiki/Electronic_cigarette