The permanent joining of materials through the use of heat and/or pressure is referred to as?

The correct choice is Welding because it specifically refers to the process of permanently joining materials, usually metals or thermoplastics, through the use of heat and/or pressure. In welding, high temperatures are created to melt the workpieces together (fusion), or pressure is applied to bring them close enough for them to join without melting. This process results in a strong, lasting bond that is integral to many construction and manufacturing applications.

The other options, while related to joining processes, differ in significant ways. Soldering typically involves joining materials at a lower temperature than welding, using a filler metal with a lower melting point to create a bond, and is usually used for electrical connections rather than structural joints. Brazing, like soldering, uses a filler material to join the metals but occurs at higher temperatures than soldering, yet lower than welding, and it does not involve melting the base metals. "Joining" is a broader term that encompasses all methods of joining materials, including welding, soldering, and brazing, but does not specifically pinpoint the heat and pressure methods inherent to welding.