What FM term defines the amount and rate at which a frequency-modulated signal deviates from the center frequency?

The term that accurately defines the amount and rate at which a frequency-modulated signal deviates from the center frequency is frequency deviation. In frequency modulation (FM), the carrier signal's frequency varies according to the amplitude of the input signal, leading to deviations from its central frequency. This deviation is crucial for determining how well the information is transmitted; it encompasses both the extent and the dynamic aspects of the frequency changes.

Understanding frequency deviation is instrumental in assessing the fidelity and range of FM signals. For example, larger frequency deviations typically result in a higher signal-to-noise ratio and better transmission quality, allowing for more robust communication over varying distances and conditions.

The other choices, while related to frequency modulation, do not accurately describe this particular aspect. Frequency shift generally refers to any change in the frequency of a signal but does not specify the deviation from a center frequency in the same way. The frequency modulation index indicates the relationship between the frequency deviation and the modulating frequency but does not define the deviations themselves. Signal deviation is a less commonly used term and can lead to confusion about its specific meaning in the context of modulation techniques.