To peek means to look at something quickly or secretly, usually when you're not supposed to or when you're trying not to be noticed. When you peek through a crack in a door, you're taking a quick, careful look without opening it all the way. During hide-and-seek, you might peek through your fingers while counting to see if anyone's still running to hide.

The word suggests a furtive, brief glance rather than a long, open stare. You might peek at the last page of a mystery novel to see how it ends (even though it spoils the surprise!). A student might peek at the clock during a long test. On your birthday, you might try to peek into the closet where presents are hidden.

Peek is also used as a noun: “Take a peek at this!” means “look at this quickly.” People sometimes say sneak peek to describe an early look at something before it's officially revealed, like a sneak peek at a new movie.