Geez is an exclamation people use to express surprise, frustration, or mild annoyance. You might say “Geez, that test was harder than I expected!” or “Geez, can you believe how much snow fell overnight?”

The word works like a verbal eye-roll or a quick release of emotion. It's softer than many stronger exclamations, which makes it useful when you're startled or irritated but don't want to sound too harsh. If your little brother keeps interrupting your homework, you might sigh and say “Geez, I'm trying to concentrate!”

Sometimes people use it to show amazement at something impressive: “Geez, you really finished that whole puzzle by yourself?” The tone of your voice changes the meaning. Said with wonder, it shows you're impressed. Said with exasperation, it shows you're fed up.

Some people think geez is a mild way of avoiding a stronger word, so it may not feel completely polite to everyone. But many people use it to express a strong feeling without using language that might get them in trouble.