A malfunction is when something stops working the way it's supposed to. When your computer freezes in the middle of a game, that's a malfunction. When a vending machine takes your money but doesn't give you a snack, it's malfunctioning.

Malfunctions happen with machines and technology: a printer that jams, a fire alarm that goes off when there's no fire, or a spacecraft's navigation system that gives wrong readings. Sometimes malfunctions are minor annoyances, like a calculator that won't turn on. Other times they're serious problems, like when an airplane engine malfunctions mid-flight.

The word can also describe when body parts or systems don't work correctly. Doctors might say someone's kidneys are malfunctioning if they're not filtering blood properly, or that a patient has a heart malfunction if the heart isn't pumping as it should.

People don't usually malfunction in the literal sense, though you might jokingly say your brain is malfunctioning when you're exhausted and can't think straight. The word really belongs to machines, equipment, and biological systems that have stopped doing their jobs correctly.