Worn-out describes something that has been used so much it no longer works properly or looks decent. Your favorite sneakers become worn-out when the soles develop holes and the laces fray from months of playing outside. A worn-out pencil eraser stops erasing cleanly and just smears graphite across the page instead.

The term applies to objects that have served their purpose well but have reached the end of their useful life. A worn-out couch might have springs poking through the cushions. A worn-out bicycle chain might slip and skip instead of turning the gears smoothly. These things haven't broken suddenly; they've gradually deteriorated from repeated use.

People can feel worn-out too, meaning exhausted from working hard or doing too much. After running around at recess, swimming for an hour, and then helping your parents with yard work, you might feel completely worn-out by dinnertime. Unlike objects, though, people who feel worn-out can recover with rest and sleep.

The hyphen matters here: worn-out (with a hyphen) describes something directly, as in “worn-out shoes,” while worn out (without a hyphen) describes what has happened to something, as in “those shoes are worn out.”