A Pod system is the term used to describe a device that used a plastic pod for a tank rather than a removeable glass tank. These started as a pre filled system that did not require any maintenance but has evolved into different forms
Prefilled Pod - These systems use a pod that has a coil and liquid inside. The user simply purchases a new pod when the last is finished. Pulls the old pod out and puts a new pod in. Traditionally these are draw activated
Refillable Pod - Like the prefilled but requires the user to refill with their chosen eliquid.
Refillable interchangeable coil Pod - The user can change the coil and the liquid
Adjustable Pod systems - These come with adjustable power etc to tailor the experience to the individual using it.
Pod Mod - Is a device that comes with a pod but can be used as a mod with a tank (sometimes with the use of an adapter)