Does the network diagram usually refers to the physical layout of the network cable and devices?

No, a network diagram typically refers to a logical representation of a network, illustrating how devices and systems communicate with each other. It highlights the relationships and configurations among various components, such as routers, switches, and servers, rather than their physical layout. While a physical network diagram may depict the actual placement of cables and devices, the term "network diagram" generally encompasses both logical and sometimes physical aspects depending on the context.