What is a ping?
Sorry, I don't know.
A ping is when one FReeper alerts one or more other FReepers to a thread, or to a specific post on a thread.
You can do this by hitting the blue "Reply" under someone's post, which brings up a reply form. Then you list multiple names in the "To:" box and write "Ping" in the "Your Reply" box. The recipients will receive a link to the thread on their "ping" page.
You can access your ping page by going to the top of the Forum and clicking on the word "Ping". It will bring up a page listing every post you have made and every reply or ping others have sent to you.