A lot of you guys have listed just "heights," and then aren't clear on whether or not it counts.
If you are on a tall building's roof and standing near the edge, and a wind comes by and nearly flings you off the fucking thing, and you think, "Oh, that was scary," you're not acrophobic, you're normal. OTOH, if you step onto the roof and are in the dead middle of it, and suddenly expect that the building will twitch or an earthquake will come and toss you down, or that you might trip and stumble the 27 steps needed to reach the edge of the building and THEN fall, well that's probably an irrational fear. Maybe.