Pet trading is when you exchange your Neopet for someone else's Neopet via the transfer system. Usually members set up trades on the Neopound boards when advertising their UFT (up for trade) pet. Other users will then "offer" their UFT pets for the one in question and the board creator has the option to either accept or reject the offer.
So, have you ever done it before? I haven't, but I have tried. And if you do trade pets, do you trade them for permies or do you just continue to trade and retrade when you get tired of the pet?
For me, I would only trade my pet for a permie. I think it's pretty pointless to retrade your pets over and over again, and a bit cruel. (yes, I know they're just virtual pets but I take them pretty seriously since I can't have pets irl)