Liguy is right, but there's more to it than that. First is the purity of the copper. Many high end cables use 6 nines (99.9999%) pure copper. Then there's the oxygen free part--it has to be pulled and assembled in an oxygen free environment or it will corrode and degrade over time. Next is the the thickness of copper or as you point out overall gauge. Construction or design is another important aspect--most high end cables are not 4 gauge single strand (none that I know of). Most are many strands individually insulated to reduce skin effect. Then there are some subtle nuances, like are all the strands the same gauge or are they different so that the skin effect is different and therefore not perceptable. Then there's the dielectric that interacts with the copper. So there is a lot to these cables. Unfortuately, there are some manufacturers that relie on niavity of newbies to this hobbie. They hype a bunch of mumbo jumbo and tell you their cable is far better than anything else out there for 1/10 the price. They talk about many of these design features--but the final test is listening. Try different cables (the cable company has an extensive library where you can check out cables and find out what works for you). Forget all the mumbo jumbo and just listen--buy the one in your budget that sounds best.
