The signal spectrum refers to the range of frequencies that a signal occupies in the frequency domain. It represents how much of the signal's energy is distributed across different frequencies, which can be visualized using a graph. This concept is crucial in fields like telecommunications and audio processing, where understanding frequency components helps in signal analysis and processing. In the context of Fourier Transform, the signal spectrum is derived by transforming a time-domain signal into its frequency components. This allows engineers and scientists to identify specific frequencies, assess signal quality, and design filters to enhance or suppress certain aspects of the signal, improving overall performance in various applications.