Appendix:Fan terminology
HSOWA is an acronym that stands for Hot Skitty On Wailord Action. It is derived from the fact that Skitty and Wailord can breed in the games despite the massive size difference. It has reached cult status on some message boards, such as GameFAQs and the Serebii.net forums.
The term originates from GameFAQs where, when this topic came up, the user Endgame reportedly said "HOT SKITTY ON WAILORD ACTION!". The name then stuck.
Strangely, though Skitty is quite small, another Pokémon in the same egg group as both Skitty and Wailord, Diglett, is even smaller, at 0'8". The reason that there is no HDOWA is possibly that Diglett and Wailord are not found in the wild in the same region, thereby only being together in the National Dex listing, not one of the regional Pokédex listings, as Skitty and Wailord are in the Hoenn Dex.
The reason why Wailord is included in the Ground egg group, the same group Skitty is in, in the first place is that whales are mammals, which is what most members of the Ground egg group is comprised of. Size is no hinderance.
Trivia
This acronym could just as easily stand for 'Hot Seedot On Wailord Action', as Seedot is even smaller than Skitty and it's still in the Ground Egg Group.