some simple questions about cables.

First of all: thanks to those who answer.
I've got the point as for the difference between "interconnects" and "speaker" cables.
I 've some other questions:
a) is the so called "unbalanced" connection the most common and used one?
b) unbalanced connection means through XLR plugs?
c) what does "single ended" mean?
d) if i go in the "shop" for used interconnects cables, what specifications of the seller should i check to make sure they fit my system (Audio Research CLassic30+LS2,Rogers LS3/5??
Thank you

a) Yes
b) No - XLRs are used for balanced cables, RCAs for unbalanced cables which are also called single-ended
c) Single-ended means unbalanced and will be terminated with RCAs
d) Let's wait till someone that knows these products well can answer you. I suspect you can use either balanced or unbalanced between the ARCs, and either of spade, banana, pins or bare wire for termination of the speaker cable.

Hmm...Enrico became Fabio.