What is the Portal Cloud? Think of it like an Extranet. It’s just a password-protected web site for your customers, partners, suppliers or any external resources. On this site you can update them all with new materials, announcements, distribute leads, manage rebate programs, track customer service tickets, etc… And Salesforce CRM has this feature built in! More examples of the Salesforce Portal Cloud include:
The ForceBrain.com Custom Portal allows Salesforce customers to extend all CRM objects, and/or custom objects to their customers, partners, suppliers, or any external resource. The ForceBrain.com approach encompasses the following steps:

The Portal Cloud enables Salesforce customers to leverage their Salesforce CRM system to communicate online securely, with their customers, partners, suppliers, or any external resource.
The Salesforce Partner Portal allows Salesforce customers to extend the Sales Cloud, namely accounts, contacts, leads, opportunities, to their partners.
The Salesforce Customer Portal allows Salesforce customers to extend the Service Cloud, namely cases & solutions, to their customers.
The Salesforce Self-Service Portal allows Salesforce customers to extend solutions to their customers.