Excise - SSI Exemption Pls Help

 Hi People,

Everywhere we have studied about Notification No.8/2003 as amended by 8/2007 of Excise relating to SSI Based Exemption. Even I am well versed with the whole Notification.

But what I want to ask is what is a SSI. As in what criteria should an organisation or a company should fulfill to be eligible to be called as a SSI.

Detailed Criterias would be appreciated