A few concepts are essential for a thorough understanding of virtual networking. If you are new to vSphere, it is helpful to review these concepts.

Physical Network
A network of physical machines that are connected so that they can send data to and receive data from each other. VMware ESXi runs on a physical machine.
Virtual Network
A network of virtual machines running on a physical machine that are connected logically to each other so that they can send data to and receive data from each other. Virtual machines can be connected to the virtual networks that you create when you add a network.
Opaque Network
An opaque network is a network created and managed by a separate entity outside of vSphere. For example, logical networks that are created and managed by VMware NSX ® appear in vCenter Server as opaque networks of the type nsx.LogicalSwitch. You can choose an opaque network as the backing for a VM network adapter. To manage an opaque network, use the management tools associated with the opaque network, such as VMware NSX ® Manager or the VMware NSX API management tools.
Physical Ethernet Switch
A physical ethernet switch manages network traffic between machines on the physical network. A switch has multiple ports, each of which can be connected to a single machine or another switch on the network. Each port can be configured to behave in certain ways depending on the needs of the machine connected to it. The switch learns which hosts are connected to which of its ports and uses that information to forward traffic to the correct physical machines. Switches are the core of a physical network. Multiple switches can be connected together to form larger networks.
vSphere Standard Switch
It works much like a physical Ethernet switch. It detects which virtual machines are logically connected to each of its virtual ports and uses that information to forward traffic to the correct virtual machines. A vSphere standard switch can be connected to physical switches by using physical Ethernet adapters, also referred to as uplink adapters, to join virtual networks with physical networks. This type of connection is similar to connecting physical switches together to create a larger network. Even though a vSphere standard switch works much like a physical switch, it does not have some of the advanced functionality of a physical switch.
Standard Port Group
Network services connect to standard switches through port groups. Port groups define how a connection is made through the switch to the network. Typically, a single standard switch is associated with one or more port groups. A port group specifies port configuration options such as bandwidth limitations and VLAN tagging policies for each member port.
vSphere Distributed Switch
A vSphere distributed switch acts as a single switch across all associated hosts in a data center to provide centralized provisioning, administration, and monitoring of virtual networks. You configure a vSphere distributed switch on the vCenter Server system and the configuration is propagated to all hosts that are associated with the switch. This lets virtual machines maintain consistent network configuration as they migrate across multiple hosts.
Host Proxy Switch
A hidden standard switch that resides on every host that is associated with a vSphere distributed switch. The host proxy switch replicates the networking configuration set on the vSphere distributed switch to the particular host.
Distributed Port
A port on a vSphere distributed switch that connects to a host’s VMkernel or to a virtual machine’s network adapter.
Distributed Port Group
A port group associated with a vSphere distributed switch that specifies port configuration options for each member port. Distributed port groups define how a connection is made through the vSphere distributed switch to the network.
NIC Teaming
NIC teaming occurs when multiple uplink adapters are associated with a single switch to form a team. A team can either share the load of traffic between physical and virtual networks among some or all of its members, or provide passive failover in the event of a hardware failure or a network outage.
VLAN
VLAN enable a single physical LAN segment to be further segmented so that groups of ports are isolated from one another as if they were on physically different segments. The standard is 802.1Q.
VMkernel TCP/IP Networking Layer
The VMkernel networking layer provides connectivity to hosts and handles the standard infrastructure traffic of vSphere vMotion, IP storage, Fault Tolerance, and vSAN.
IP Storage
Any form of storage that uses TCP/IP network communication as its foundation. iSCSI and NFS can be used as virtual machine datastores and for direct mounting of .ISO files, which are presented as CD-ROMs to virtual machines.
TCP Segmentation Offload
TCP Segmentation Offload, TSO, allows a TCP/IP stack to emit large frames (up to 64KB) even though the maximum transmission unit (MTU) of the interface is smaller. The network adapter then separates the large frame into MTU-sized frames and prepends an adjusted copy of the initial TCP/IP headers.