Stinky means having a bad or unpleasant smell. When your gym shoes get stinky after weeks of soccer practice, they've developed that sharp, sour odor that makes people wrinkle their noses. Garbage left in the sun becomes stinky. So does a litter box that hasn't been cleaned, or milk that's gone bad in the refrigerator.

The word is informal and a bit playful, which is why you'll hear it more often in casual conversation than in formal writing. A scientist might describe an odor as “putrid” or “malodorous,” but most people would just call it stinky. Young children often call things stinky when they're just learning to notice and name different smells.

Some things are naturally stinky, like skunks (which spray a terrible-smelling liquid to defend themselves) or durian fruit (which smells so strongly that it's banned from some hotels in Asia, even though many people love how it tastes). Other things become stinky over time: wet towels left in a heap, a kitchen trash can that needs emptying, or sweaty sports equipment.