A microtemperament is a temperament where the consonances sound justly intoned to most listeners in ordinary musical use. The allowed errors in the approximated ratios are therefore somewhat context-dependent but would typically be less than 2.8 cents.
A JI tuning might be microtempered to increase the number of available concords or to regularise the scale for some purpose such as allowing more full-width continuous frets on a stringed instrument. Microtemperament may also be used to introduce deliberate slight mistunings to avoid phase-locking when a JI tuning is implemented on an electronic instrument.
A microtemperament may be equal, linear, planar or of any dimension less than that of the JI scale being approximated.