An e-cigarette, or electronic cigarette, is an electronic device that converts nicotine liquid into water vapor. The e-cigarette has three main parts: a battery, atomizer, and cartridge. The battery, the largest part, has an indicator light on one side and it screws onto the atomizer. The heart of every e-cigarete is the atomizer, which converts the e-liquid into smoke. The cartridge, a cylindrical inhaler that contains the e-liquid, attaches to the atomizer.