The signal to metasignal ratio of a work is essentially the ratio
of volume of content to volume of descriptive information about the work itself.
The term is a variation on the much-quoted signal to noise ratio (which describes the amount of actual worthwhile content in an online community as compared to worthless garbage) widely used these days. Unlike the S/N ratio, however, the S/M ratio has no equivalent in the natural physical world, and cannot be described in any way as a quality of a data channel. It is, however, a property of most protocols for data transfer, equivalent to how many bytes of actual information are ordinarily sent per byte of information used for upkeep and control of the data stream itself. Similarly the s/m ratio of a file format would be the average number of bytes of document information vs. document content. The best example of an s/m ratio would be the amount of data about a program accessible through the program's online help system divided by the amount of data about the program's online help system accessible through the program's online help system.
On Everything, the S/M ratio would be described as the ratio of nodes to metanodes-- i.e. the number of nodes based in information about the outside world for each node about everything itself.
For some reason i actually went and decided to measure a vague approximation of e2's signal to metasignal ratio. I went and hit "random node" a hundred times, and wrote down the number of nodes (actual information about the outside world) and metanodes (nodes about using everything, nodes based on everything inside jokes, and nodes involving specific e2 noders). I wound up with 3 metanodes out of a hundred, leaving Everything with an s/m ratio of 97/3 in the nodes i saw, about 32.3 (this was purely measuring number of nodes; if each writeup is treated as an independent entity, the ratio came to 123/4, or 30.75). Note, however, this number doesn't mean much of anything; because of the nature of everything, the way the metasignal affects the viewer is rather skewed. Thing is, while metanodes may be more rare, they are much less likely to be dirt nodes. They tend to be softlinked a great deal more heavily, and therefore more easily found. Moreover, they are a lot more popular; looking inside the recent C! list while writing this node revealed 6 metanodes out of 50, for a much lower ratio of 44/6 (7.3 or so). As a result, anyone actually using e2 will wind up perceiving a much higher effective s/m ratio.
Either way the s/m ratio, like the s/n ratio of any system is only useful when addressed not as an absolute measured numerical value, but as a relative value compared to other systems. Also note that in the end the s/m ratio doesn't say anything useful. While very high s/m ratios are generally a good thing, and very low s/m ratios usually an indicator of some problem, s/m ratio says nothing about quality; low s/m is only bad if the metasignal itself is bad. Look at, for example, Slashdot. Slashdot has so much signal that the metasignal is dwarfed numerically; however, since the metasignal (complaints about moderation, "why was this posted" garbage, personal attacks on the slashdot sysadmins, etc.) is so grating and distracting, the reader finds it hard to ignore the metasignal and thus perceives the s/m ratio as a lot lower than it really is. Meanwhile compare this to Forum 2000, where the s/m ratio of the SOMAD responses rarely dips above 1, but where the metasignal is so entertaining that the reader rarely if ever thinks of it as a problem.
In the extremely rare case a work has nothing but sheer content, with no information of any kind within itself describing itself, it can be said to have no S/M ratio. (Calculating the S/M ratio of a work with no metasignal would result in dividing by zero.) This kind of occurrence is not often seen, however, except in simple things such as signs and fliers; even in the case of something such as a book with no interesting self-referential content, you have a relatively small amount of metadata consisting of things like the page of copyright information, the author's name, and the title of the book itself.
Conversely, if some work or online forum reaches the point where it contains absolutely nothing other than metasignal, it can be said to have an S/M ratio of zero. In such a case, completely everything present in the system would describe the system itself, with no content which is applicable outside the scope of the system or which is original. An S/M ratio of zero would mean that no new information is incoming and that all that remains is for what exists to be churned around and stagnated. Such an event can be thought of as the online messaging system equivalent of heat death.