To impinge means to have an effect on something, usually by limiting it or pushing against it in an unwanted way. When something impinges on you, it's making an impact you didn't invite.

If your neighbor's tree branches impinge on your yard, they're reaching over the fence into your space. When a new rule impinges on students' free time, it cuts into hours they used to have for themselves. The word often carries a sense of intrusion or interference: something is crossing a boundary or affecting something it shouldn't.

You'll often hear impinge paired with “on” or “upon.” A loud party might impinge upon your ability to concentrate on homework. Government laws can impinge on citizens' freedoms when they become too restrictive. In science, light waves can impinge on a surface, meaning they strike or hit it.

The word suggests a kind of encroachment: one thing pressing against another's territory, rights, or space. When you tell someone “that impinges on my plans,” you're saying their request or action is bumping up against something you already had in place. While impinge can be neutral (like light hitting a mirror), it most often describes something unwelcome pushing its way into where it doesn't belong.