Waterproof means protected against water so that no moisture can get through. A waterproof jacket keeps you dry in a downpour because water beads up and rolls off instead of soaking through the fabric. A waterproof phone case can let you take pictures underwater without ruining your device, as long as you follow its depth and time limits.

The word suggests very strong protection: water cannot easily penetrate the material. A water-resistant watch might survive a splash but fail if you go swimming. A waterproof watch, however, is designed to handle being underwater to a certain depth. Sailors have used waterproof materials for centuries to protect cargo during ocean voyages, and today's waterproof technology ranges from simple waxed canvas to sophisticated synthetic materials.

You'll find waterproof gear everywhere water poses a threat: hikers wear waterproof boots through streams, campers sleep in waterproof tents during storms, and construction workers use waterproof covers to protect building materials. The opposite of waterproof is porous, which means full of tiny holes that let water seep through.

When manufacturers call something waterproof, they mean it is built to keep water out under specific conditions, which are usually explained on the label. That distinction matters when you're caught in a rainstorm miles from home or when you're protecting something valuable from getting soaked.