An ache is a dull, steady pain that lasts for a while. Unlike a sharp, sudden pain from bumping your knee or cutting your finger, an ache settles in and stays. Your muscles might ache the day after you've played hard or tried a new sport. Your head might ache when you're getting sick or haven't had enough water. A toothache throbs persistently until you get it treated.

The word can describe emotional pain too. When you miss someone you love, you might feel an ache in your chest, not an actual physical pain but a real feeling of longing or sadness. When you ache for something, you want it deeply, like aching for summer vacation during a long winter, or aching to see a friend who moved away.

Aches are your body's way of telling you something needs attention: rest, water, medicine, or time. They're usually not emergencies, but they're uncomfortable enough that you can't ignore them. The achy feeling you get with the flu can make you want to curl up under blankets until you feel better.