What is a digital signal?

A digital signal represents data as discrete values, which means it conveys information in binary format—typically in the form of ones and zeros. This characteristic allows digital signals to maintain their integrity over long distances and be less susceptible to noise and degradation compared to analog signals. Digital signals use specific voltage levels to signify these discrete states, making them highly reliable for transmitting data in electronic systems.

In contrast, continuous waveforms characteristic of analog signals (the first option) portray varying voltage levels over time, which can lead to more signal degradation and noise issues. Fluctuating voltage levels, as mentioned in the third option, also refers to an aspect of analog signals, where the signal can vary smoothly between a range of values instead of being defined in discrete steps. The fourth option, a type of AC waveform, again relates more to analog signals, as AC waveforms represent fluctuating currents and voltages rather than the binary representation of data inherent to digital signals. This is what distinguishes digital signals from the alternatives presented in the other options.