In brief, someone who adheres to the upper class "WASPy" lifestyle of New England or the United Kingdom (keep in mind the prep lifestyle is not explicitly limited to these areas). Preps almost always come from "old money" families and attend or have attended preparatory schools.
Preps work hard and play hard, showing a keen interest in academics as well as sports, particularly English sports such as Golf, Tennis, Polo, Squash, Sailing, etc.
Ivy League educations are common among preps, although it is said by some that some of the smaller, liberal arts colleges in the northeast such as Amherst are far more preppy than Harvard could ever be. The equivalents across the Atlantic include Cambridge, Oxford, and to a lesser extent, the Sorbonne in France.
Contrary to popular belief, preps do not wear mall-brand clothes from Abercrombie & Fitch, Hollister, American Eagle Outfitters, and Aeropostale, but from classic brands such as L.L. Bean, J. Crew, Ralph Lauren, Brooks Brothers, Burberry, J. Press, and Lacoste. The preppy looks is sophisticated, yet understated. Since most preps come from wealth, their privilege is appreciated, but not flaunted.
There are certain concepts that are essential to being preppy, including (but not limited to): having appreciation for sport, knowing why wearing sandals in the middle of a rainy October day is just plain fun, and that "summer" is a verb, not just a noun.
I know this so well because I am one of these "preps".
Guy 1 is an avid tennis player, went to St. Mark's, now attends Yale, summers at Nantucket, and likes Brooks Brothers suits. Guy 1 is a prep.
Guy 2 likes Monday Night Football, goes to Putnam Public High, and wears Abercrombie hoodies with American Eagle Outfitters Jeans. Guy 2 only THINKS he is a prep.
The ultimate phone, remains the only world's first touchscreen phone with the largest pool of applications, the most sensitive screen interface, and capabilities that never stop improving.
86% of people who talk crap about iPhones do so because they are jealous and cannot afford one.
Guy with dumbphone: "iPhones are stupid, you pay hundreds of dollars just to use something that you could have had for $20 a month"
iPhone User: "What are you talking about? These things are great, I can check my emails, take great photos, listen to my music, play app games, surf the web at any time, watch YouTube at any time, and so much else!"
Guy with dumphone: "....I know"