In the most general sense, a musical tuning is a particular selection of frequencies from the infinite variety available in the pitch-continuum, generally ranging in number (cardinality) between 5 and about 72 individual notes. Of course it is possible for a tuning to have thousands of pitches, but practicality and the jnd generally place the upper limit around 200 to 300 pitches.
In a more particular sense, a tuning references the particular frequencies chosen by an instrument manufacturer as part of the design of the instrument, and in the case of some instruments, such as stringed instruments like the guitar or violin, the particular frequencies the performer may choose for the individual strings.
A tuning is a particular tuning of [the] generators and periods [of a certain tone-space] -- RMS optimal, TOP, etc.
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