Geekvape Rebuildable Deck Atomizers (RDA) and Rebuildable Tank Atomizers (RTA) are both types of rebuildable tanks. They allow you to build your own coil to your desired resistance and attach it to the deck, rather than using prebuilt coils as you would in a traditional tank.
RDAs – These have a deck on the bottom of the atomizer where the coil attaches, and you manually drip e-liquid onto the wick. RDAs lack a tank, so they will only hold as much e-liquid as the cotton of the wick can absorb.
RTAs – These have a tank, as you find on a traditional vape tank. This combines the customizability of building your own coil with the convenience of having a tank to hold more e-liquid.