An odor is a smell, especially one that's strong or unpleasant. When you walk past a dumpster on a hot day and wrinkle your nose, you're reacting to its odor. When you open the fridge and discover forgotten leftovers have gone bad, that distinctive smell is an odor.

The word odor is neutral, meaning it can describe any smell, but people most often use it for smells that are noticeable or bothersome. A scientist might study the odors that attract mosquitoes to humans, while a detective might notice the odor of smoke at a crime scene. Your gym bag develops an odor if you leave sweaty clothes inside too long.

Sometimes people use odor to sound more scientific or formal than just saying “smell.” A doctor might ask about unusual odors as a symptom of illness. An environmental inspector might investigate odors coming from a factory.

While fragrance suggests something pleasant like flowers or perfume, and stench means something truly awful, odor sits in between: a smell strong enough to notice, whether it bothers you or not.