Leak means for liquid or gas to escape slowly through a hole, crack, or opening where it shouldn't. When your water bottle has a tiny crack, water leaks out and makes everything in your backpack wet. When a roof leaks during a rainstorm, water drips through damaged spots into your house. A leaking tire slowly loses air until it goes flat.

The word also describes the unwanted flow itself: “There's a leak in the basement pipe.” Finding leaks can be tricky because they often start small. A dripping faucet wastes gallons of water over time, and a small gas leak can become dangerous if no one notices it.

Beyond physical leaks, the word describes information escaping when it's supposed to stay private or secret. When details about surprise party plans leak out, someone accidentally (or purposely) tells the birthday person. When classified government documents leak to reporters, private information becomes public. A person who deliberately shares secret information is called a leaker. In this context, to leak something means to reveal it, usually to journalists or the public, often anonymously or without permission.