This image compares various communications channels. The thickness of the lines between boxes is a rough indication of channel capacity or bandwidth. The top image represents something familiar to users of computers in the old days, who remember the modems for sending data from one computer to another using telephone lines. My first modem was actually 300 baud and I remember spending hours just to transfer a one megabyte master’s thesis from home to university computer.
The second image represents fast broadband cable, which could transfer the same file in seconds. Now what about social bandwidth? Consider four bilingual Europeans who must communicate one-to-one, never in larger groups. Let us consider that these are not highly educated people with a few words in many languages, but simple peasant farmers who speak to languages only because they live very near the shared national borders.
How well will the Swede who also speaks Finnish communicate with the Lithuanian who also speaks Latvian? That depends on the sequence of intermediates. If the Swede tries to speak to the Russian whose only other language is Latvian, the use of simple gestures and the odd cognate word might allow the level of understanding shown by the thin line between them. That would also be true of the Finn and Lithuanian.
On the other hand, the Finn who also speaks Russian will have no trouble whatsoever holding a discussion with the Russian who speaks Latvian. Despite that one good connection, the overall level of communication between Swede and Lithuanian would be low, slow, awkward and unreliable.
The bottom image shows an entirely different situation. The Swede talks to the Finn in their common language, Finnish. The Finn and Russion speak Russian, as in the previous case. But now the Russian speaks with the Lithuanian, using their one common language, Latvian. There would be some miscommunication, as whenever intermediaries are used, but the overall communications channel is good.
This illustration is reproduced elsewhere, on the Social Network Optimization website, but the emphasis on that site is on interpersonal relationships, not on communication.
Even though this example has nothing to do with computers, it can be seen that the term bandwidth is appropriate. It seems best to refer to it as social bandwidth to emphasize that it has something to do with interpersonal communication in the social network.
This website is concerned with maximizing social bandwidth and is related to Social Network Optimization, which involves Social Combinatorics and other methods, as applied to the work on Social Systems.