Vape Tanks have a reservoir to hold e-liquid, and replaceable coil head that converts the e-juice into vapor. Pods are tanks in various shapes that use proprietary connection types and usually have a built-in coil. Mouth To Lung tanks produce a small amount of vapor and have a restrictive draw that mimics that act of smoking, whereas Direct To Lung tanks are more comparable to small fog machines with airflow that allows you to inhale straight through it.
Vape Tanks come in a variety of sizes, but they all consist of two main components: a reservoir to hold e-liquid, and the replaceable coil head that turns the e-juice into vapor. The metal and wick will gunk up and break down over time, so the coils need to be replaced every 2-4 weeks depending on use. Most tanks now use the standard 510 threads, meaning they can be used across various mods and device, however, sub-ohm tanks should only be used with appropriately powered mods.
Restrictive tanks that mimic the act of smoking where you first gather a mouthful before inhaling are classified as Mouth To Lung. Tanks with open airflow that allow to inhale straight through are known as Direct To Lung. DTL tanks are generally larger, and produce a much bigger cloud so they have a higher power requirement as well. MTL tanks vary greatly in size but they can get quite tiny, and the clouds are much smaller.