The RG cable is way of labeling the different design types that have been used since the beginning of radio.
This link has a brief post on the types. Hope this helps.
[Link: therealcableguy.com]

Yeah, me neither.

Once I read what I wrote, as you correctly quoted it, it looked like a slam. So sorry about that! It wasn't an insult. I was trying to say that it is so hard to grasp what's going on with transmission lines that it makes sense that you (and I, as I said) don't understand it. The tools to understand it don't make much sense themselves. Sorry it came out as an insult!