Ojou (お嬢), pronounced o-joe (often Ojou-san or Ojou-sama, as they are the more formal honorifics), a formal Japanese word for literally "young lady", is typically used in anime when referring to wealthy, high-class female characters.
Oftentimes, a wealthy Ojou is found in a leading role in the Absurdly Powerful Student Council. In fact, her wealth is often the Hand Wave explanation for the absurd power: they make the rules because they have money.
In the original Japanese, expect all types of ojou to use the more formal first-person pronoun "watakushi" rather than the neutral "watashi" or the more casual (and feminine-only) "atashi," and to make heavy use of the "wa" feminine emphasis particle at the end of their sentences.