Collapsible means able to be folded down or compressed into a smaller, more compact form. A collapsible umbrella folds up small enough to fit in a backpack, while a collapsible chair can be flattened and stored in a closet. The key idea is that something collapsible can shrink down when you're not using it, then expand back to full size when you need it.

Engineers and designers create collapsible objects to solve a practical problem: how do you make useful things easier to carry, store, or transport? A collapsible telescope lets astronomers pack up their equipment after a night of stargazing. Collapsible shipping containers can be folded flat for the return journey, saving enormous amounts of space on cargo ships. Even something as simple as a collapsible laundry basket makes life easier by tucking away when empty.

The word comes from collapse, which means to fall down or cave in. But when we say something is collapsible, we usually mean it's designed to fold up on purpose, not that it's weak or broken. A collapsible ladder is sturdy when extended but cleverly engineered to compress when you're finished with it.