Short - and I completely disagree with the above post. Long hair in great condition can look ludicrous if it simply doesn't suit that person. Short hair suits lots of women of all different sorts of looks, not just the types mentioned by noxlumos.
I class 'short' as anything from chin-length and shorter.
A pattern I've noticed - many women on TV, say, start off with short hair and they look great - then they grow it out and end up looking a bit identikit and generally not as cute as when it was short. Kylie Minogue's hair is growing back and right now it looks terrific but I'm betting she'll continue to grow it back to its previous length.
Short hair for me is a head-turner - I see short hair, I automatically look, same with red hair (dyed or natural). When I see short red hair on a woman, I'm rooted to the spot!