To blink means to close and open your eyes quickly, usually without thinking about it. Your eyes blink automatically about 15 times per minute to keep them moist and clean, sweeping away dust and spreading tears across the surface. You barely notice yourself doing it, but if you try to stare without blinking, your eyes start to feel dry and uncomfortable within seconds.

People also blink when they're surprised or trying to clear their vision, like when you step from a dark room into bright sunlight. You might blink rapidly when something startles you, or blink in disbelief when you hear unexpected news.

The word can also describe anything that flashes on and off quickly. A turn signal on a car blinks to show which direction the driver plans to go. A cursor blinks on a computer screen to show where you're typing. Warning lights blink to grab your attention.

When someone says something happened “in the blink of an eye,” they mean it was incredibly fast. A moment of inattention can be called a blink: if you blink, you might miss something important happening right in front of you.