1. So, what is this type all about?
Aquatic-type is an idea promoted by Saiph-Charon, initially on reddit, later on Deviantart and 4chan:
This idea supposes that Water-type, due to its sheer abundance, should be split into two categories, one refering the element of Water, and other referring the existence of being in water.
Fundamentally, this follows in line of Water being split into three Egg Groups depending on their body types.
2.Where does this name come from?
The name is supposed to match Flying-type in terms of theme and idea, referring to being a swimmer, rather than a Water elemental. It also follows with Telefang and Digimon's classification of Water elemental species.
3. Does this type have an in-game source?
As stated before, Water-type is abundant and large. This would help to cut it in half
4. What would be the ideas behind such a type?
Aquatic type would use moves that utilize water, rather than summoning water. Species in it would be aquatic and swimming animals, rather than Water elementals.
5. What would be the type interactions of such a type?
Mainly, it would act as a balancing type for other types, like Ice. Water covers for a large variety of situations, so this would cut them.
6. What would be the distribution of such a type?
Large as Water, actually. Perhaps even more.
7. Future comments: