Ought means should or must, expressing what's right, necessary, or expected. When you say “I ought to study for tomorrow's test,” you're recognizing that studying is the right thing to do, even if you'd rather play video games. When someone says “You ought to apologize,” they mean an apology is what the situation calls for.

The word carries a sense of obligation or moral responsibility. It's stronger than simply wanting to do something but softer than absolute commands. If your parents say you ought to help with chores, they're not just suggesting it casually: they mean it's your responsibility, part of being in a family.

Ought often appears when we're thinking about what's fair, wise, or decent. “She ought to win the spelling bee” means she deserves to win based on her preparation and skill. “This ought to work” means you have good reason to expect success.

You might write “Students ought to respect their teachers” in an essay, while casually telling a friend “You should totally try that new pizza place.” Both express the same basic idea, but ought sounds more formal.