What term defines the change in frequency caused by modulation in an FM transmitter?

In an FM transmitter, "deviation" is the specific term used to describe how far the carrier frequency moves away from its resting (center) frequency when an audio signal is applied. The louder the audio input, the greater the frequency deviation. "Modulation index" is a related but distinct mathematical concept; it is the ratio of the maximum frequency deviation to the frequency of the modulating audio. Therefore, it does not define the raw change in frequency itself. Terms like "shift" are typically reserved for digital modes (like Frequency Shift Keying or FSK), and "spectrum spread" relates to spread-spectrum techniques. Deviation is the correct fundamental term for analog FM.