To facilitate collaboration across corporate boundaries, Salesforce offers Salesforce Communities. The licence for communities come in three flavours: customer community, customer community plus and partner community. There are similarities and differences between the entitlements.
The biggest difference can be seen between customer community and customer community plus. There's a simple rationale behind it: a customer community account uses simplified sharing access, so the computational load to determine access of potentially millions of users stays reasonable and easy to grasp for administrators:
All licences, full Salesforce or one of the community licence types, access the same data, in the confines of the entitlements. So it's NOT different products, just different permissions on the Salesforce platform.