Just my take on it, when factory tanks came out that use premade coil heads that started offering bigger airflow and multiple coils for direct lung they adopted the term 'subohm tank'. Up until then most factory coils were for mtl tanks and had resistances ranging from 1-2.8 ohms. The bigger airflow with heftier coils and bigger cloud production were all ones you had to build yourself. They took direct lung and cloud chasing mainstream with easy factory coils people didn't have to build/wick. Technically any tank with a resistance below 1 ohm is a subohm but it helps differentiate between one you build yourself and one you pop premade coils into.
As others said, rta is a rebuildable tank. The deck accepts only individual coils whether you make them yourself or buy them in a package from geekvape or demoncoils or buy them handmade from folks who sell them. It's a separate coil and you have to wick it. An rda is the same in terms of installing coils then wicking them but lacks a tank, it's just a top cap with no chimney.
They started using the term 'rba' for addon decks to subohm tanks like the smok tfv8 baby beast, big baby etc. In place of the factory coil head they made a small velocity type deck that fits them and allows you to convert the subohm tank to an rta. Rba is just a generic term that covers anything you can rebuild yourself, whether it screws into a baby beast, whether it's a serpent smm or a dead rabbit. On something like the baby beast, if using the rba deck it's essentially an 'rta' since it becomes a rebuildable tank. True rta's or those usually called rta's are exclusively build it yourself. If you opt to use the premade cartridges with coils and wick already stuffed inside, just screw in and go, it's a subohm tank.
Rta's, rdta's, rsa's and rda's are all included under 'rba' since they're all rebuildable by the user. Ie you can tinker with the coil/wick separate. The other terms just go further to differentiate what type of ReBuildable Atomizer it is. Is it a tank, a squonk compatible, a plain dripper, a dripper with a tank below the deck.