Mass region

Any region in a resonator where removal of material will increase the frequency of a specified resonance. Mass regions are typically those regions of relatively high amplitude. For a half-wave axial resonator, the mass regions are confined approximately to the front and back 1/8 wavelength of the resonator. For nonaxial resonances, the mass regions may be located elsewhere.

Also see —
Mass
Stiffness
Stiffness region