To reek means to smell absolutely terrible. When something reeks, it doesn't just smell bad: it produces such a powerful, unpleasant odor that people notice it immediately and want to get away from it. A gym locker room might reek of sweat after a basketball tournament. A trash can left in the sun for days will start to reek. If you forget your lunch in your backpack over a long weekend, it might reek by Monday morning.

The word suggests something beyond ordinary bad smells. A single banana going brown has an off smell, but a dumpster behind a restaurant reeks. When your dog rolls in something disgusting at the park, they might come home reeking of whatever they found.

People also use the word figuratively to describe situations that seem obviously wrong or corrupt. If a teacher gives easier tests to favorite students, you might say the situation reeks of unfairness. When someone tells an obviously made-up excuse, their story might reek of lies. In these cases, something “smells wrong” even though there's no actual odor involved.