The word down has several distinct meanings:

1. A direction opposite to up. When you walk down the stairs, you're moving toward a lower level. When the sun goes down, it sets below the horizon. A bird flying down from a tree branch descends toward the ground.
2. Not working or functioning. When a computer network goes down, it stops operating and people can't access it. When a website is down, visitors see error messages instead of web pages. Teachers might say the classroom projector is down if it won't turn on.
3. Feeling sad or discouraged. Someone might feel down after losing a game or missing out on something they wanted. A friend who seems quiet and withdrawn might be feeling down. This is different from clinical depression, but it can describe temporary low spirits.
4. Soft, fluffy feathers found under the outer feathers of birds, especially ducks and geese. Down keeps birds warm because it traps air close to their bodies. People use down to fill winter coats and comforters because it provides excellent insulation while staying lightweight.
5. In American football, one of four chances a team has to advance the ball ten yards. A team on first down has just received the ball or made a first down. By fourth down, they usually punt or attempt a field goal unless they're close to gaining those ten yards.