For the most part, you can go to the reference link and read up what is out there, as there are many information on the web now a day. But because there are so many information and versions, it can be confusing for the most of us. This link from wikipedia will provide some useful information for reference; http://en.wikipedia.org/wiki/Copper_wire_and_cable
This refers to the purity of the copper. The “N” stand for “Nine” or “9” and a 4N rating mean it is 99.99% pure. 6N rating mean 99.9999% pure.
OCC is a term very common in the audio world but what is common may not necessary correct. The full name should be PCOCC which stand for Pure Copper Ohno Continuous Casting and later, most refer to mostly just OCC which is trademarked in 1986 by professor Ohno of Chiba Institute of Technology in Japan for Ohno Continuous Casting and is a format or type of process used to product high grade copper wires and not a type of copper wire per say. Because this type of process produce high grade copper wires, some company later on refers it as OCC wire.
OFC stand for Oxygen-free copper and OFHC stand for Oxygen-free high thermal conductivity and both are copper that have been refined with very little oxygen left in them. Under the IACS standard, later on many refers the high grade OFC copper as 4N copper. For further detail and information, please refer the wikipedia link; http://en.wikipedia.org/wiki/Oxygen-free_copper
MCC stand for Mono-crystal Copper. This is also sometime refer to as single crystal and or long grain crystal copper. In the audio world, this is the best type of copper to be use. But due to the process of manufacturing mono-crystal copper is relative new, various industries and technologies refers the material as mono-crystal or single crystal copper or silver pending on their application. In the audio world, it would refer as Mono-crystal where as in semiconductor industry would refer to as single crystal. For more detail, please refer to the wikipedia link; http://en.wikipedia.org/wiki/Monocrystal
In the mid eighty, we have the OCC process developed and in the nineties, we have the OFC developed and the “N” graded coppers. In the late twenties, we have the MCC developed. Each process has improved the pervious material somewhat and brings it close to its purest form.
Other then copper, many other mineral material are used to manufacture audio cables and connectors. Material are selected mainly due to electronic connectivity, effect on audio property and cost. Material like zinc, tin, gold, silver, platinum and rhodium etc.. are used also.