Leisure = The least formal. Includes all athletic-wear and shorts. Jeans are usually leisure, and always when worn with athletic shoes, message t-shirts, and sweatshirts (including polar fleece).
Casual = Nicer, but still fairly relaxed. Due to geographical variations, I prefer to not define this category too precisely. Lunch with your boss, your pastor, or your grandma requires casual clothing. Business casual fits here.
Business = Formal business clothing is mostly suits and "jacket outfits", sometimes tailored skirts or dresses.
Social = Clothing for social occasions includes floral dresses such as those worn by wedding guests, cocktail dresses, and ball gowns.
At times, especially out here in the Great Northwest, I have been known to lament the lack of opportunities to get dressed up (see my previous post,Flashback). When I ask you what I should wear, I don't want to know if I can wear my jeans. Can I wear my ball gown?