An object or part that's welded together can't be taken apart easily. Think of two metal pieces attached with welding.
A weld is usually strong and permanent, so it's often used to describe something fixed in place – a bridge might have a steel beam welded underneath. When you see someone repairing a bike, they might use a welder to join the broken parts back together. It can also mean that people or things are connected closely, like two friends who are welded together through thick and thin.
To join two materials (especially two metals) together by applying heat, pressure and filler, either separately or in any combination.
To wield.
