To complain means to express dissatisfaction or annoyance about something you think is wrong or unfair. When you complain about the cafeteria food, you're voicing your unhappiness with it. When your friend complains that the math homework is too hard, she's expressing frustration about the assignment.

Everyone complains sometimes, but there's an important difference between complaining productively and just whining. If you tell your teacher, “This assignment is confusing. Could you explain it again?” you're identifying a problem and seeking a solution. But if you just moan, “This is so hard!” without trying to improve the situation, you're simply venting frustration.

Some people become complainers, constantly finding fault with everything around them: the weather's too hot, then too cold; the game is boring, then too competitive. Constant complaining can drain energy from everyone nearby and rarely fixes anything.

The word can also have a formal meaning: to make an official statement that something is wrong. A customer might file a complaint with a store about a broken product, or a neighbor might complain to the city about a pothole.