MOD - An APV (Advanced Personal Vaporizer). Allows for adjustment of Voltage/wattage. Has battery protection. Removable rechargeable battery.
RBA - ReBuildable Atomizer. A tank that can be rebuilt as in replacing the coil and wick.
RDA - Rebuildable Drip Atomizer. Similar to the RBA but there's no tank. Drip a couple of drops into the RDA, vape a couple draws, drip again, vape again, etc.