To breach means to break through or violate something that's supposed to protect or contain. When a dam breaches, water forces its way through a crack or weak spot, flooding the land beyond. When enemy soldiers breach a castle wall, they smash through defenses meant to keep them out.

The word often describes breaking rules or agreements. A breach of contract happens when someone fails to do what they promised in a legal agreement. A security breach occurs when someone breaks into a computer system or building they shouldn't access. When you breach someone's trust, you break a promise or betray their confidence in you.

A breach can also be the gap or opening itself. If there's a breach in the fence, animals might escape through it. Whales breach when they leap dramatically out of the water and crash back down, literally breaking through the surface. In all these cases, something that was whole, secure, or protected gets broken or violated, whether it's a physical barrier, a rule, or a promise.