Memes are a worldwide social phenomenon. The more a meme resonates with people, the more they'll share it and the farther it will spread. Memes are usually funny, but often that humor is injected with wry political or social commentary. Sometimes memes exist for shock value or to teach a life lesson. Other times a single photo or short video will generate hundreds of hilarious interpretations. Sometimes a meme will be appreciated by only a select group of people, and other times a meme will have near-universal appeal. Here's a look at some popular meme categories and examples to give you a better idea of the breadth and scope of these viral statements.