Electronic nicotine delivery systems are commonly known as e-cigarettes but are also known as e-cigs, vape pens, e-hookahs, e-pipes, tanks, mods, vapes, and more.
Some are made to look like regular cigarettes, cigars, or pipes. Larger devices such as tank systems do not resemble other tobacco products. And some resemble pens, USB sticks, and other everyday items.
E-cigarettes can be open or closed systems.  Open systems require the user to add an e-liquid.  Closed systems use pre-filled cartridges or pods.