An electrical conductor is any material through which electrical current flows easily. Most metals are good electrical conductors, with silver the best and copper second. Most wire conductors are copper due to its low cost, although aluminium and silver are also used sometimes. The copper may be tinned with a thin coating of solder, which gives a silvery appearance. Tinned wire is easier to solder for connections. The wire can be solid or stranded. Solid wire is made up of only one conductor.
Stranded wire is made up of several individual strands put together in a braid. Some uses for stranded wire include telephone cords, extension cords and speaker wire, to name a few. Stranded wire is flexible, easier to handle, and less likely to develop an open break. Sizes for stranded wire are equivalent to sum of areas for the individual strands.
Heavier wires generally are in an insulating sleeve, which may be rubber or one of many plastic materials. General purpose wire for connecting electronic components is generally plastic coated hookup wire. Hookup wire that is bare should be enclosed in an insulating sleeve called spaghetti.
Twisted pairs are used for small signal applications in electronics. They may or may not be shielded. They are good in preventing magnetic field pickups. The shielded ones are used especially in low noise applications.