The word hi is a casual, friendly greeting people use when they meet or see each other. When you walk into class and say hi to your friend, you're acknowledging them in a warm, informal way. It's shorter and more relaxed than hello, which makes it perfect for everyday situations like passing someone in the hallway or answering the phone when your grandparent calls.

You'll use hi dozens of times a day without thinking about it, but it's worth noticing when not to use it. In very formal situations, like meeting your school principal for the first time or addressing a letter to someone important, hello or another formal greeting may work better. But for friends, family, teachers you know well, and most everyday encounters, hi is just right: simple, genuine, and welcoming.