In blogging, ping is an XML-RPC-based push mechanism by which a weblog notifies a server that its content has been updated. An XML-RPC signal is sent to one or more "ping servers," which can then generate a list of blogs that have new material. The technology was first introduced by Dave Winer to Weblogs.com in October 2001. Today, most blog authoring tools automatically ping one or more servers each time the blogger creates a new post or updates an old one (source: .wikipedia.org)
In simple terms, "pinging" is the simple act of alerting other websites that new content has been published on your blog.
The Primary purpose of pinging your blog is two-fold: 1. to generate internet traffic to your blog, 2. to build backlinks to your blog.
Most wordpress blogs will automatically ping http://rpc.pingomatic.com/
every time new content is posted.
Many experts would agree that you should ping as many available resources as possible when you add new content.
One way to do this effectively is to use a service such as pingler.com, pingoat.com, or pingomatic.com.
I would suggest using pingler.com and adding their plugin to your blog to ensure that your content is "pinged" on a regular basis.
Hope this helps,