Microtonality is a term without a clear definition. It is sometimes used to describe music that uses intervals less than a normal half-step in width. But it is also sometimes used to describe non-Western music that cannot be easily notated or understood in terms of the familiar 12 tone equal temperament system that dominates Western music.
Microtonality is a distinctly Western concept, as many forms of traditional music use intervals that don't fit into 12-ET, and these intervals are considered a normal part of music.
Microtonal music is frequently discussed alongside the idea of xenharmony, but the two are distinct concepts, and microtonal music does not necessarily sound xenharmonic, even to people unfamiliar with it. Some tunings which would normally be considered microtonal, when used to play familiar musical intervals from diatonic scales and Western music, can be more in tune to natural harmonics, leading to music that sounds more consonant and in-tune.
With a fundamental step size smaller than a quarter-tone in Western music, 31 tone equal temperament is unambiguously microtonal by all definitions.
I personally see 31-ET as a logical and natural window into microtonal music, more so than quarter tones or 24-ET.
These resources deal with microtonal music in general; although 31-ET is certainly a popular tuning among microtonal composers and performers, only a small portion of the total microtonal repertoire deals with 31-ET.