“What’s up?” is one of the most common informal greetings in American English. It's a casual way to ask a friend or acquaintance what they are doing or how they are feeling. Think of it as a relaxed version of “How are you?” or “What’s new?”

While many people associate the phrase with the cartoon character Bugs Bunny and his famous line, “What’s up, doc?”, its origins go back further. The phrase appeared in print as early as the 19th century, used to ask what was wrong or what was happening. However, Bugs Bunny's popularity in the 1940s helped turn it from a question of concern into the casual, everyday greeting we know today.

“What’s up?” is best used in informal situations. You can say it to friends, family members, or colleagues you know well. It would be out of place in a formal setting, like a job interview or a business meeting.

Responding to “What’s up?” is also simple. Common replies include:

• “Not much.”
• “Nothing much.”
• “Hey.”
• “What’s up?” (saying it back)

If you are actually doing something interesting, you can share it. For example, “Not much, just getting ready to see a movie.” But a short, simple response is perfectly fine and very common.

Understanding these small phrases is a big step in sounding more natural when you speak.