According to Wikipedia pinging means following:
In blogging, ping is an XML-RPC-based push mechanism by which a weblog notifies a server that its content has been updated.[1] An XML-RPC signal is sent to one or more “ping servers,” which can then generate a list of blogs that have new material. Many blog authoring tools automatically ping one or more servers each time the blogger creates a new post or updates an old one.
Briefly said pinging notifies a server about updates of your content of your blog. That specific server will generate list of newly updated blogs and let people know about it.
