An electronic cigarette, also known as an e-cigarette or an e-cig, is an electrical device that simulates the act of tobacco smoking by producing an inhaled vapor bearing the physical sensation, appearance, and often the flavor (with or without nicotine content) of inhaled tobacco smoke, without its odor or, ostensibly, its health risks. The device uses heat (or in some cases, ultrasonics) to vaporize a propylene glycol- or glycerin-based liquid solution into an aerosol mist, similar to the way a nebulizer or humidifier vaporizes solutions for inhalation.
The device's components usually include a small liquid reservoir, a heating element, and a power source, which may be a battery or a wired USB adapter. Most electronic cigarettes are portable, self-contained cylindrical devices in varying sizes, and many are designed to outwardly resemble traditional cigarettes. Most are also reusable, with replaceable and refillable components, though some models are disposable. Liquids that produce vapor for electronic cigarettes are available in many different flavor varieties and nicotine concentrations, including nicotine-free versions.