Mods can refer to both the actual e-cigarette, also known as a personal vaporizer, or PV. There can also be mods for other parts of e-cigarette hardware, such as a cartomizer tank mod.
Mods sort of came into being to offer an alternative to the basic cigarette sized e-cigarettes on the market. While these devices are great at mimicking cigarettes, they may leave something to be desired in the performance department. By creating their own e-cigarettes, modders were able to use replaceable batteries that offered much better battery life and performance. Mods come in all shapes and sizes and offer users a wide choice in power output (voltage).