RDA / RTA / RBA are atomizers that make use of DIY rebuildable atomizer coils. These are for advanced vapers only. An RDA is a Rebuildable Dripping Atomizer, these use custom coils where you drip drops of e-liquid directly onto the wick. RBA atomizers are Rebuildable Atomizers with tanks to hold the e-liquid. An RTA is a rebuildable tank atomizer, these becoming quite popular.