A pinched tail is one that is not well spread...a very tight, closed tail. You want the main tail feathers to not over-lap much showing a good depth from top of tail to bottom.
For example in Ameraucanas you want a fairly fanned out tail. and when you look at it from the side it resembles a fan that you would use on yourself. I often think of the Asian hand fan things that you see. but with a pinched tail it looks like that fan is folded up.
I consider this hen to have a fairly pinched tail
this hen as well
this is the best example of a fanned tail that I have had from an Ameraucana in the past