What is slang? Slang is informal language. It can offend people if it is used about other people or outside a group of people who know each other well. Slang is usually used in speaking rather than writing. Slang normally refers to particular words and meanings but can include longer expressions and idioms. Slang is also vocabulary that is used between people who belong to the same social group who have relationship. Slang is Words, phrases, meanings of words, etc commonly used in ...