Do not take my post as an answer. Your question is good. Here is what I *think* it means.

Strong post flop play would be using every bit of leverage you can get on your opponent. That includes, reads, knowledge of odds and pot odds and using them, ability to lay down when you “read” you are beaten OR ability to bluff your opponent into laying down his hand, etc. I can’t think of anything else but I am sure others will list more.

Pre flop play is talked about so much because it is relatively simple compared to post flop play.