Rda is a dripper, rta is a tank with a rebuildable deck like a dripper. Sub ohming is anything lower than 1ohm, subtanks are made by kanger. Tanks that can sub ohm like the Atlantis only have premade coils, tanks like the delta 2 or subtank can use the rebuildable coil or premade coils. Tanks like the lemo are only rebuildable.