Social norms are the informal, unwritten rules that guide acceptable behavior in a group or society. Deviance refers to behavior that violates these norms. There are two main types of deviant behavior - formal deviance that breaks laws, and informal deviance that violates unwritten social rules. Examples of deviant behaviors include alcoholism, drug addiction, eating disorders, underage drinking, and acts that are considered deviant in some societies but not others, showing how norms can vary between groups. Deviance is important because it helps define normative behavior and maintain social stability, though what is seen as deviant differs in each society.