To weld means to join pieces of metal together by heating them until they melt and fuse into one solid piece. When a welder works on a car frame or a ship's hull, they use intense heat (often from electricity or gas) to make the metal so hot that it becomes liquid at the edges. When it cools, the separate pieces have become permanently joined, creating a bond that's often as strong as the original metal.

Welding is everywhere in modern life. The bridges you drive over, the buildings you walk into, the bicycles kids ride: most metal structures depend on welding to hold them together.

Welders wear dark protective masks because the light from welding is incredibly bright and can damage your eyes. Those showers of sparks you might see at a construction site? That's welding in action.

As a noun, a weld is the place where the pieces were joined. The word can also describe bringing other things firmly together: a good team captain might weld different players into a unified group.