google always put his eye on every website. when he found some one in unethical way of promotion then he punished your site. In this case ranking of your site is going down are totally finished. this situation is cold google penality.
When you don't follow the rules of Google & promote your website from unethical ways than Google penalized your site. When site get penalized than site ranking get dropped & there is multiple tools by which you can check whether your site is penalized or not.
Simply put ... it is a penalty you attract from Google when you use questionable tactics to publish and promote your website online.
There are 3 types of Google Penalty's: 1. Sandbox: This is a penalty given to new sites in which your site is indexed by Googling (Site:yourdomain.com), but does not rank for any keywords. This can last from 2 weeks to up to 9 months. 2. Temporary Ban: This is a penalty given to sites that for some reason or another broke a rule like duplicate content, spamming, or other black hat tactics. This will last until your site is fixed. You can resubmit your site for approval through Webmaster tools. 3. Permanban: This is the ban of all bans. This can be found by Googling (Info:yourdomain.com), and nothing shows up even though your site has been live for months. All in all, you gotta obey the rules, or risk getting sent to hell.
There's a new announcement how Google is including in its algorithm a penalty for sites that have bad customer service.