A gap is an empty space between two things, or a difference that separates them. You might notice a gap between your front teeth, or a gap in a fence where a board is missing. When you're reading and come across a word you don't know, that's a gap in your knowledge.

Gaps can be physical spaces, like the gap between train cars or the gap under your bedroom door. But they can also be invisible differences. A generation gap describes how parents and grandparents sometimes see the world differently than kids do. A pay gap means some people earn less money than others for similar work. When your soccer team is losing by three goals, you might say you need to “close the gap” to catch up.

People also use gap to describe missing pieces or breaks in time. If someone takes a gap year between high school and college, they're taking time off to travel or work. A gap in someone's memory means they can't remember part of what happened. When a speaker pauses too long during a presentation, that awkward silence is a gap in the conversation.

The word often suggests something that needs filling or fixing, though sometimes gaps serve a purpose: the gap between a subway train and the platform keeps them from scraping together, and the gap in your schedule gives you time to relax.