Linux Administration Cookbook

namespaces

Without starting a trend, here's the Linux Programmer's Manual again:

"A namespace wraps a global system resource in an abstraction that makes it appear to the processes within the namespace that they have their own isolated instance of the global resource. Changes to the global resource are visible to other processes that are members of the namespace, but are invisible to other processes. One use of namespaces is to implement containers."

In practice, this means that your singular network interface can have multiple namespaces attached to it, which the utilizing processes will believe is the sole instance of that device. 

Network interfaces aren't the only example, but they're one of the more obvious candidates as every VM needs ...