What does SeeD stand for...?

[Qurange]

I doubt that they're the only Sorceresses in the world, just the only visible ones.

And it's pronounced 'seed'--as I recall, it was originally partially a joke in the Japanese, in which 'seed' and 'Cid' are pronoucned the same way.

But for in-game reasoning, (as an edit), yeah. SeeDs grow in the Garden, as has been said elsewhere.