Which of these describes a fusion of edges during welding without the use of filler metal?

The term that describes a fusion of edges during welding without the use of filler metal is fusion welding. This method involves heating the base materials until they reach a molten state, allowing them to flow together and solidify as one piece. In fusion welding, the process relies solely on the heat generated by an energy source to achieve the necessary temperatures for welding, without the addition of any external materials to fill the joint.

While techniques such as arc welding, spot welding, and laser welding may also involve fusion processes, they can include the use of filler material or have specific applications where they might not strictly adhere to the definition of fusion welding. Fusion welding is a broader category that encompasses various techniques, and the key characteristic is the joining of materials through the melting and solidification process without additional filler.