The word behind describes where something is when it's at the back of something else, out of direct view. If you're standing in line at lunch, the person behind you is the one you can't see without turning around. When a teacher writes on the board, the students sit behind her. A squirrel might hide behind a tree trunk, using it as a shield.

Behind also means running late or falling short of where you should be. A student who misses a week of school might fall behind in math, needing extra work to catch up. If your soccer team is behind by two goals, you're losing and need to score to tie the game. A project that's running behind schedule isn't finishing as quickly as planned.

You can also leave something behind, meaning you forgot it or moved on from it. You might accidentally leave your backpack behind in the cafeteria, or deliberately leave behind old habits as you grow and mature.

The word captures both physical position (where something is) and progress (how far along you are). Whether you're looking behind you to check who's there or working hard not to fall behind on your responsibilities, the word always suggests something that's back there, either in space or in progress.