Invisible means unable to be seen. When something is invisible, light passes through it or around it in a way that makes it impossible for your eyes to detect. Air is invisible: you breathe it constantly but never see it. Glass can seem nearly invisible when it's very clean, which is why people sometimes walk into sliding glass doors by accident.

Scientists use invisible to describe things like certain light waves (infrared and ultraviolet light are invisible to human eyes, though some animals can see them) or microscopic organisms too small to see without special equipment.

People also use invisible figuratively to describe feeling overlooked or ignored. A student might feel invisible if teachers never call on them, even when their hand is raised. Groups of people can feel invisible when society doesn't acknowledge their experiences or contributions. When someone says a problem is invisible, they mean people aren't noticing or paying attention to it, even though it's real and important.

The opposite of invisible is visible. Some stories feature invisibility as a superpower or magical ability, like in H.G. Wells's novel The Invisible Man or the Greek myth of Perseus, who wore Hades's cap of invisibility. The fantasy appeals to people because being invisible would let you observe without being observed, though the stories usually explore how that power creates as many problems as it solves.