Excuse means to forgive someone for a minor mistake or to free them from a duty or obligation. When you accidentally bump into someone in the hallway and say “excuse me,” you're asking them to overlook your small error. Teachers might excuse students from class for a doctor's appointment, meaning they give permission to be absent without penalty.

An excuse (as a noun) is also the reason you give for why something happened or why you can't do something. If you're late to practice, you might offer an excuse: “My bus broke down.” Some excuses are valid explanations of real problems, but others are just attempts to avoid responsibility. When someone makes up weak excuses for not doing their homework (“my dog ate it”), people stop believing them.

There's an important difference between a genuine reason and a flimsy excuse. A reason explains what actually prevented you from doing something. An excuse often tries to shift blame or avoid consequences. If you tell your friend you'll help them with a project but then make excuse after excuse for why you can't, they'll notice you're not being reliable.

The phrase “no excuse for” means something is completely unacceptable: “There's no excuse for being mean to others.” This means nothing justifies that behavior, no matter what reasons someone might offer.