Plinking to me refers to just playing around without any real purpose other than fun with no real restrictions... thus the tin cans and dirt clod targets. Keeping a tin can bouncing across the ground is plinking. This activity is not done at a range, but at an informal spot such as the back 40 at my in-law's.

Shooting at a true range, with formal rules, restricted targets, and range safety officers is not plinking to me. If I go to the range, it is for a purpose, i.e. to zero a rifle or shoot a known distance range.