I've read all that but it's simply an asteroid (minor planet would be a bad name). If a large rock the size of meteor approached our planet tomorrow, we would not, under any circumstances, call it a minor planet / planet / star / dwarf planet in common usage. In fact, as Obesebear said, from a scientific point of view even meteor is incorrect. It's a large rock / asteroid that has become a meteoroid (when it lands it is a meteorite). But in common usage, meteor is fine.
In terms of what Aerith would use, I think large rock is a good trade-off. 8)
edit. Although Meteor is much larger than a meteoroid.
Long story short: Meteor is an asteroid if it came from an orbit (which seems to be the idea) or a large rock if not. Let's face it, it doesn't even look like a normal rock because it appears to have magical abilities (likely the writers wanted it to look that way since the Black Materia summoned it). Plus, in FF7, as daft as it sounds, all celestial bodies are ALIVE. Yup... that's right. It isn't just their planet that "speaks", it's the stars, asteroids, you name it.
