RBA - Rebuild-able atomizer. Encompasses all variations of rebuild-able device
RDA - Rebuild-able dripping atomizer. Typified by a short, 510 base, sufficient to hold a coil or coils, with a small juice well to drip juice into via the drip tip. Often the most flavorful, and most often used for sub-ohm vaping.
RTA - Rebuild-able tank atomizer. A liquid tank that surrounds and feeds the atomization chamber.