From TheBestCaseScenario

[edit] What soldering is..

When the need comes to join parts into a whole, soldering helps. Be it when you are into plumbing, metal working or circuits.. Soldering is the process where you use a fluid bonding agent to "glue" together metal parts, but need to keep some property the metals had before: thermal conduction, electrical properties or the ability to be air/water-tight.

[edit] Soldering in modding

Soldering in modding can take at least 2 shapes:

[edit] Electronic work

This is where soldering irons and soldering paste and flux come together. Using the right tools, materials and parts can yield a functional circuit. In this case, soldering is the process of fixing electronic components, like chips, resistor, capacitors etc on a board, or a PCB. Solder paste and tin in general is electrically conducting and also glues the parts with metal like prowess on the board, offering them a certain amount of protection.

[edit] Metal work

In case you are building a heatsink, a waterblock or something else that requires good joints, the process of soldering is when you use solder paste to better bond the metals together, in order to avoid water leaks, make better thermal contact or.. something else you might think, maybe give physical resistance or something..