The term RDA is a bit loose in the vaping world, but you can rest assured that the correct term is rebuildable dripping atomiser because this type of product is used for dripping E liquid onto the coils.

Rebuildable Dripping Atomizers are for those looking to build to their own preference as you're able to alter certain components to tailor the experience for cloud chasing or better flavour. Originally, RDAs were designed for mechanical mods but nowadays you can use them on regular devices due to the support of low ohm resistances.