An uplink portgroup will have NICs mapped from multiple hosts and is required for external communication. Distributed portgroups are the one that are created internally for the VM and VMkernel traffic.
Thank you for your response!
1. You mention "NICs mapped from multiple hosts", this "nic" refers to the network card on the virtual machine?
2. In the VDS there only has one uplink port group, in order to achieve "NICs mapped from multiple hosts", so we divide the "uplink port group" into several "uplink". I understand it right?