~

The ~ (tilde) sign when attached to a ratio is commonly used to mean tempered. For example, the generator of the meantone temperament can be denoted by ~3/2.

When it is used to connect multiple ratios, it means that the ratios are tempered together. For example, the whole tone in the meantone temperament can be denoted by 9/8~10/9.

It can also be used before a harmonic series chord (a:b:c:...) in order to indicate that the chord is being approximated (tempered) by some temperament.