Classic archetype that generally refers to a rich, beautiful, but stuck up, demanding girl.
They're commonly tsunderes with the stuck up demanding side being the tsuntsun side.
As far as actual world meaning Ojou refers to "My Lady/Mistress/etc"
A similar meaning and spelled word (so similar some folks mix them up) Oujo means Princess litterally.
They do have a regal air ,but dealing with them if you're a common guy might not be the easiest thing. They're infamously hard to impress. (They may end up going after you show them the best local ramen place by saying "My Chef can make better than this!")
The opposite type personality wise is the Hime-sama .
Nagi Sanzenin (Hayate no Gotoku! / Hayate the Combat Butler!)
Louise (Zero no Tsukaima)
Ai Emma from Jigoku Shoujo
Most rich girls with drill hair
among a few others.