What is meant by pinging your blog or website

Pinging is the process of making the search engines know that your site has been updated.
Especially blogs which are of course updated weekly or sometimes daily have to be pinged often.
There are a lot of pinging services available in the net like www.autopinger.com, www.bloggers.com, www.pingomatic.com etc.
What you have to do is to type your website URL in these websites and they will ping your website or blog for you.