There are many different types of e-cigarettes. Those that contain nicotine in cartridges or refill fluids (sometimes referred to as e-juice) are often marketed as “nicotine delivery devices”.
Others are marketed as electronic cigarettes even when they contain no nicotine. Instead, moistening agents such as propylene glycol or vegetable glycerin are inhaled, along with flavourings such as sugar and alcohol.
E-cigarette devices produce no real smoke and are sold as devices that can be used anywhere because there’s no risk of second-hand or passive smoking. It’s unclear, however, whether “vaping” has second-hand effects, particularly if the fluids contain nicotine.