Welding is a manufacturing process that fuses two or more parts together by applying heat, pressure, or both, forming a joint after the parts cool. Welding is commonly used for metals and thermoplastics, but can also be used for wood. The completed joint can be called a weldment.

Some materials require specific processes and techniques to be used. There are some materials that are considered “unweldable”, a term not usually found in dictionaries but very useful in engineering.

The parts being joined are called parent materials. The materials added to help form the joint are called fillers or consumables. These materials can take the form of materials called parent plates or tubes, filler wire, consumable electrodes (for arc welding), etc.