Words and phrases occurring primarily in speech and informal writing that seeks a relaxed, conversational tone. "My favorite chow is a burger and a shake" or "This math exam has me wired" may be acceptable in talking to a roommate, in corresponding with a friend, or in writing a humorous essay for general readers. Such choices of words, however, would be out of place in formal writing--in, say, a laboratory report or a letter to your senator. Contractions (let's, don't, we'll) and abbreviated words (photo, sales rep, TV) are shorthand of spoken language. "Good writers" use such expressions with an awareness that they produce an effect of casualness.