Question: can anyone please explain me what is meant by salesforce?
 and what is meant by Partner portal?
i tried to figure it out but there is no use could any one help me out..

Answer: 
Salesforce in it's core is a combination of features (clouds) that are focused on CRM, suppored by a platform that will also allow you to extend these features, or build entirly independant functionality. It's oriented to be used by internal users of a company.

The partner portal or partner community is a feature of salesforce that allows giving access to users in companies your company works together with, so that collaboration can be done within your CRM system. The benefit is that both your internal as external partner users can work directly on the same data, which is a huge benefit.

Partner community can for instance be used to give access to re-sellers or offshore support teams (as part of another organisation).
You can find more information on partner portal at <https://help.salesforce.com/HTViewHelpDoc?id=partner_portal_about.htm&language=en_US>

As explained at that link, partner portal is no longer offered to new customers. They have been replaced by Communities. You can find more information about them at <http://help.salesforce.com/help/pdfs/en/salesforce_communities_implementation.pdf>

You can use full-blown SalesForce internally to deal with leads, customer accounts, customer support, and then leverage Communities to deal with partners for sales and support.