It seems that ‘polyphonic’ can mean a number of different things indeed, even though at least in the VCV Rack manual it reads:
If your module supports polyphonic inputs or has polyphonic outputs, then it can be considered a “polyphonic module”, so add the “Polyphonic” tag to the module’s manifest.
To me, this definition may work for developers, but I find it less useful in practical terms for a user.
Therefore, I would also like to open the following thought for discussion:
One major differentiation I find helpful in praxi is by the type of signal that is being processed polyphonically, i.e. whether it is 1.) Control Voltage (CV) signals or 2.) Audio signals. The latter I would call ‘(audio) effect’ modules.
I am aware that current definitions don’t really specify this distinction, possible because in the end, everything merges into being ‘Voltage’ anyway.
Moreover, the issue is complicated by the dilemma that module tags sometimes appear to be rather arbitrary as they do not seem to be curated rigorously.
The taxonomy used in the ‘Utilities for polyphonic channels’ list attempts a more practical approach. There still are inconsistencies in there, too, but it is at least an attempt to give the term ‘polyphonic’ a bit more granularity from the perspective of the user. Hence the view there is more for practical purposes, from ‘what do I want to achieve’ to ‘which module can I use for that’.