What is a PING?
Ping is a computer network tool used to test whether a particular host is reachable across an IP network; it is also used to self test the network interface card of the computer, or as a speed test. It works by sending ICMP “echo request” packets to the target host and listening for ICMP “echo response” replies.
Source : Wiki
Since you know what a ping is now,In English that means :
Ping services allow you to automatically notify blog directories and search engines that your blog has been updated.
Yes, your next question is how on earth do you notify all those sites that you have a update on your blog? Seems a bit of a drag isn’t it? Well, its actually pretty easy. WordPress has allows you to state a list of websites that you want to ping automatically when there is a update on your blog. How do you do this?
Head on to your wordpress dashboard -> Settings -> Writting => Update Service
WordPress has a couple of default websites that it will ping when you update but you should add on a whole lot more to stand a chance of some traffic. The team at the Daily Blog Tips have put together list of sites that you should ping, all you need to do is copy and paste it to your site and your done!
The list is below! Enjoy 
http://blogsearch.google.com/ping/RPC2
http://1470.net/api/ping
http://api.feedster.com/ping
http://api.moreover.com/RPC2
http://api.moreover.com/ping
http://api.my.yahoo.com/RPC2
http://api.my.yahoo.com/rss/ping
http://bblog.com/ping.php
http://bitacoras.net/ping
http://blog.goo.ne.jp/XMLRPC
http://blogdb.jp/xmlrpc
http://blogmatcher.com/u.php
http://bulkfeeds.net/rpc
http://coreblog.org/ping/
http://mod-pubsub.org/kn_apps/blogchatt
http://www.lasermemory.com/lsrpc/
http://ping.amagle.com/
http://ping.bitacoras.com
http://ping.blo.gs/
http://ping.bloggers.jp/rpc/
http://ping.cocolog-nifty.com/xmlrpc
http://ping.blogmura.jp/rpc/
http://ping.exblog.jp/xmlrpc
http://ping.feedburner.com
http://ping.myblog.jp
http://ping.rootblog.com/rpc.php
http://ping.syndic8.com/xmlrpc.php
http://ping.weblogalot.com/rpc.php
http://ping.weblogs.se/
http://pingoat.com/goat/RPC2
http://rcs.datashed.net/RPC2/
http://rpc.blogbuzzmachine.com/RPC2
http://rpc.blogrolling.com/pinger/
http://rpc.icerocket.com:10080/
http://rpc.newsgator.com/
http://rpc.pingomatic.com
http://rpc.technorati.com/rpc/ping
http://rpc.weblogs.com/RPC2
http://topicexchange.com/RPC2
http://trackback.bakeinu.jp/bakeping.php
http://www.a2b.cc/setloc/bp.a2b
http://www.bitacoles.net/ping.php
http://www.blogdigger.com/RPC2
http://www.blogoole.com/ping/
http://www.blogoon.net/ping/
http://www.blogpeople.net/servlet/weblogUpdates
http://www.blogroots.com/tb_populi.blog?id=1
http://www.blogshares.com/rpc.php
http://www.blogsnow.com/ping
http://www.blogstreet.com/xrbin/xmlrpc.cgi
http://www.mod-pubsub.org/kn_apps/blogchatter/ping.php
http://www.newsisfree.com/RPCCloud
http://www.newsisfree.com/xmlrpctest.php
http://www.popdex.com/addsite.php
http://www.snipsnap.org/RPC2
http://www.weblogues.com/RPC/
http://xmlrpc.blogg.de
http://xping.pubsub.com/ping/
