Multipathing, also called I/O multipathing, is a typical feature in block-based storage (but usually for SAN environments) to establish and manage multiple physical paths between an initiator and the target device, basically to provide better availability and resilience (in case of path failures) but also to improve performance.
Objective 3.3 for VCP65-DCV and VCP6-DCV are the same just because there weren't big changes in those storage functions from vSphere 6.0 to vSphere 6.5.
For more information and details, see the vSphere 6.5 Storage guide (https://docs.vmware.com/en/VMware-vSphere/6.5/vsphere-esxi-vcenter-server-652-storage-guide.pdf.pdf).
