How can we differentiate among customer portal, partner portal and community in salesforce?

Salesforce portals and communities empower your customers and partners by providing a social forum directly related to your internal business processes so that they can connect with the right information and the right people at the right moments.

Depending on when your organization began using Salesforce, portals may no longer be relevant because they aren’t available for new organizations. Perhaps you’re still holding tight to your organization’s customer portal because it’s what you’ve always known. What you need to know moving forward is that communities are effectively upgraded portals, rebranded as communities.

With a number of features carrying over and a wealth of new enhancements, Salesforce communities allow your organization to pursue your business goals in the following ways:

Business integration: Integrate your business processes with your community to allow customers and employees to collaborate on the same records in the same space.
Social feed: Follow the records you care about most and work together with subject matter experts to resolve customer issues and close deals.
Branding and customization: Customize your communities to align with company branding and messaging. Create a community that will promote your brand and give your customers and employees a seamless experience.
Mobile: Access communities from any of your devices.
Social intelligence: Receive recommendations and content tailored for your interests and business needs within your communities.
Security and scalability: Know that your data and user information is safe with the Salesforce platform because the community is an extension of your internal organization.
Self-service: Empower your customers to help themselves to take the load off your support staff and allow them to focus on your most complex customer issues.