A constraint is something that limits what you can do or how you can do it. When you're building with LEGO bricks and run out of blue ones, that's a constraint: you have to work within the pieces you have. When your teacher says your book report can't be longer than two pages, that's a constraint on length.

Constraints aren't always bad. Sometimes they make you more creative. If you're making a video game but can only use five sound effects, that constraint might push you to use them in clever ways you wouldn't have thought of otherwise. Engineers designing a bridge work within constraints like budget, materials, and the laws of physics. Olympic sprinters push against the constraint of human speed itself.

Time is often a major constraint: you might have great ideas for a science project, but only two weeks to complete it. Money can be a constraint when your family is deciding on vacation plans. Physical space is a constraint when you're trying to fit all your books onto one shelf.

When something is done without constraint, it means there are no limits holding it back. Understanding your constraints helps you figure out what's actually possible and plan accordingly.