A mesh network is a network in which the devices -- or nodes -- are connected so that at least some, and sometimes all, have multiple paths to other nodes. This creates multiple routes for information between pairs of users, increasing the resilience of the network in case of a failure of a node or connection. In a full mesh topology, each network node is connected directly to each of the others. In a partial mesh topology only some nodes have multiple connection partners. The decision of which nodes to mesh depends on factors like the traffic pattern of the network overall and the extent to which nodes or connections are at risk of failure.
The illustration below shows a full mesh network with six nodes. Each node is shown as a sphere and connections are shown as straight lines.
The illustration below shows a partial mesh network with six nodes. Each node is shown as a sphere and connections are shown as straight lines. The connections in either a full or partial network can be wired or wireless.
Mesh networks are where the difference between logical and physical topologies is most important. Few networks today are built as full mesh networks, and yet nearly all networks today appear to be a mesh because everyone on the network can connect with everyone else. This full connectivity is a property of the network protocols and not the topology; any network can appear to be fully meshed at the logical level if data can be routed between each of its users.
Many people see wireless networks as mesh networks, but wireless networks are another example of where physical and logical topology are different. Both WiFi networks and cellular broadband networks appear to be meshed because every user can connect with all the others, but in fact there is a central node (the WiFi hub or your cellular operator's cell sites) that provide the wireless connectivity. The physical network is really a star topology but the logical connectivity is a full mesh.
The most common full mesh network today is the data center fabric, a local area network (LAN) designed to provide full bandwidth connectivity to each connected device. Wide area networks (WANs) are typically partial mesh networks or tree topologies.