A system of tuning where all intervals are derived from the pure fifth and the pure third, as opposed to temperament.

in some texts, the five-limit system of tuning; in this book, any system of tuning using low primes.

In music, just intonation, also called rational intonation, is any musical tuning in which the frequencies of notes are related by whole number ratios; that is, by positive rational numbers. Any interval tuned in this way is called a just interval; in other words, the two notes are members of the same harmonic series. Although in theory two notes tuned in the frequency ratio 1024/927 might be said to be justly tuned, in practice only ratios using quite small numbers tend to be called just; more complex ratios are often considered to be rational intonation but not necessarily just intonation.