For questions about soldering both electrical and plumbing joints.
Soldering is the process of joining two or more bits of metal together, by melting a filler material over/into the joint, and then allowing it to cool. Soldering is used to make both electrical and plumbing joints.
In electronics and electrical work, soldering is used to join two pieces of metal, often to insure electrical conductivity. This process is accomplished by heating solder with a soldering iron, allowing the molten solder to flow over the joint, and then allowing the solder to cool and harden.
In plumbing, soldering is used to create a leak free joint between two fittings. The joint is heated using a torch. Once hot, solder is melted into the joint where it cools, hardens, and creates a solid leak free joint.
Soldering VS. Welding VS. Brazing
Soldering is different from welding, because the materials being joined to not melt. It is closely related to brazing, though brazing uses a different filler material that melts at a higher temperature.