Plinking to me is any informal shooting where you're either not competing or competing with friends just for fun. You can use just about any safe target. It's also funner to play games such as shoot till you miss and other shooting games.
Sometimes you earthlings REALLY amaze me!
In a word, FUN.
Dead Bears, the only good kind.
I went Plinking with Stalkingbear, that WAS FUN. Still have a smile on my face.