What characteristic distinguishes a digital signal from an analog signal?

A key characteristic that distinguishes a digital signal from an analog signal is that digital signals represent data in discrete values. This means that digital signals consist of distinct, separate levels (often represented as bits, such as 0s and 1s) rather than a continuous range of values.

In contrast to analog signals, which can vary continuously and represent an infinite number of values within a given range, digital signals are inherently quantized. This quantization is what allows digital signals to be more resilient to noise and distortion, making them ideal for many applications in modern electronics and communications.

The other options present characteristics that are not true for digital signals. Digital signals do not vary continuously in amplitude; they operate within a finite set of values. Similarly, they do not hold infinite values, as each discrete level corresponds to a specific representation of information. Lastly, while digital signals can operate at various frequency ranges, they are not restricted to low frequencies; they can function effectively at higher frequencies as well, depending on the application and technology used.