The term "Sloane Ranger" (often pluralised to just Sloanes) refers to the lifestyle of upper-middle class young women living in West London. It was coined by British author Peter York in his book the Official Sloane Ranger Handbook (co-authored with Ann Barr). The term combines "Sloane Square" (an area of London where these women would typically live or hang out) with "Lone Ranger." The term is now applied to men as well as women. Beware: it can be used as a slur.
The archetypal Sloane Ranger was Lady Diana Spencer before her marriage to Charles, Prince of Wales.