1. A condition in which a desired resonator's resonance falls within a specified frequency band.
    Example: for a specified frequency band between 19950 Hz and 20050 Hz (i.e., nominally 20 kHz), an axial resonator is tuned when its axial resonance falls within this frequency band.
  2. A condition in which the power supply has been adjusted so that its operating characteristics match those of the stack.

The process by which either of these conditions is achieved is called tuning.