To deform means to change something's natural shape by bending, twisting, squashing, or stretching it, usually in a way that makes it less functional or attractive. When you sit on a cardboard box, you might deform it, leaving it crumpled and misshapen. Heat can deform plastic toys, warping them into strange new shapes they were never meant to have.

The word often suggests damage or distortion. A car accident can deform a vehicle's frame. Scientists study how forces deform materials: how much pressure does it take to bend a metal beam, or how does ice deform as glaciers slowly flow down mountains?

Something that has been changed this way is called deformed. A deformed coin might be bent or flattened. The process itself is called deformation.

The word carries a sense of something being pushed out of its proper form. While clay deforms easily when you work with it (which can be useful for sculpting), many things work best in their original shape. When a basketball gets deformed and won't bounce properly anymore, you know something has gone wrong with its structure.