Welding is a fabrication or sculptural process that joins materials, usually metals or thermoplastics, by causing coalescence. This is often done by melting the workpieces and adding a filler material to form a pool of molten material (the weld pool) that cools to become a strong joint, with pressure sometimes used in conjunction with heat, or by itself, to produce the weld. This is in contrast with soldering and brazing, which involve melting a lower-melting-point material between the workpieces to form a bond between them, without melting the work pieces.

Welding involves melting the base material and deposited weld metal into a homogeneous joint. If properly executed, the resulting joint material is stronger than the base material. In testing to destruction the base material should fail first in a competently welded joint.

Soldering involves forming the joint with just deposited metal at much lower temperatures. The base material is not melted in the process. The soldered joint is usually weaker than the base material. Failure would often be in the joint material outside of the base material.

Soldering's just a smaller, manual version instead of using oxygen or gas you use heat to melt the copper to solder metal together

In welding two metals are melted together where as soldering is used to fix the electrical and electronic components to specific designed boards to get a required output.

Welding --- joint metals by melting the joint.

Soldering ---- joint metals by bonding an alloy to the joint surfaces.

http://en.wikipedia.org/wiki/Welding

http://en.wikipedia.org/wiki/Soldering