Pods and tanks perform exactly the same function. You fill them with vape juice and the coil within heats the liquid so that you can vape it. But apart from the look and specification, the main difference between a pod and a tank is that generally you cannot replace the pod with that of another brand or device. The pod is purpose built for that device, unlike 510 threaded tanks which can be swapped with any of your choosing.

Also, with tanks you just need to change the coil, whereas some pods come with an in-built coil that cannot be replaced, meaning you need to replace the pod entirely when the coils lifespan expires.

Pre-filled pods come with e-liquid already inside them and are designed to be single use. Once you've used up all of the juice, it's time to dispose of the pod and replace it.

Re-fillable pods can be filled with any compatible e-liquid of your choice and used several times before you either need to change the coil or replace the pod.

Re-fillable pods are more cost effective, however some vapers prefer the covneninnce of pre-filled as they require zero maintenance.