A helix is a three-dimensional spiral shape, like a corkscrew or a spring that's been stretched out. If you've ever seen a spiral staircase wrapping around a central pole, you've seen a helix in action.

The shape appears constantly in nature. Your DNA, the molecule inside your cells that contains instructions for building you, forms a double helix: two spirals twisted around each other like intertwined ribbons. Vines climbing up a tree often grow in a helix pattern. Some seashells, like the whelk, grow in a beautiful helical spiral.

Engineers and inventors use helixes too. The threads on a screw form a helix, which is why turning the screw pulls it into wood. Some water slides twist in a helical path, and the wire inside a spring mattress coils in tight helixes. Even a strand of old-fashioned telephone cord, if you remember those, naturally forms a helix.

A helix differs from a flat spiral (like a snail shell seen from above) because it moves through three dimensions, continuously rising or falling as it curves around.