Within means inside the limits or boundaries of something, whether those boundaries are physical spaces, amounts of time, or abstract limits.

When your teacher says to finish the assignment within an hour, you need to complete it before that time runs out. When a treasure is hidden within a castle, it's somewhere inside those walls. When you stay within the rules of a game, you're playing without going beyond what's allowed.

The word emphasizes staying inside boundaries. A soccer player must keep the ball within the field of play. A story might take place within a single day. You might live within walking distance of school, meaning close enough that the school falls inside the area you could reasonably walk.

Within can also describe internal qualities or states: when you find courage within yourself, you're discovering strength that was already inside you. When something is within your abilities, you have the power to do it. The word emphasizes that whatever you're talking about exists or happens inside particular limits, without crossing over or going beyond them.