Ozma is an important, much needed lesson.

[Enkidoh]

The name is probably taken from Princess Ozma from the second Wizard of Oz novel The Marvelous Land of Oz (or, if you've never read the novels and only know of the film versions, she appears right at the end of the much maligned 80's sequel Return to Oz) - as Yasuhiro mentioned above.

Funnily enough in the original novel she was actually genderswapped into the form of a young boy named Tip and was only restored to her true form at the end - this idea of not having a true form seems to ring true with the FF Ozma's lack of form (as mentioned below).

But as Evangela mentioned, Ozma was FFIX's superboss (the supposed reason for why it was a floating sphere was that it was apparently a summon that lost it's shape because like here in XIV with Primals being a 'wish given form', the eidolons in FFIX were embodiments of myth and legend, and which would change form as the stories that gave birth to them also evolved and changed with each retelling. Hence Ozma was believed to be an eidolon (summon) whose origin stories had died out and was forgotten, and therefore lost it's shape, becoming nothing but a giant featureless multicoloured orb, perhaps showing the eidolons true form.

Anyway, that's enough FF lore-regurgitating from me. Carry on!

EDIT: Sniped by Yasuhiro