Spectral properties refer to the characteristics of signals or systems that are represented in the frequency domain. This includes the analysis of the frequency content of a signal, such as its spectral density, power spectrum, and frequency response. Spectral properties are essential in various fields such as signal processing, communications, and control systems, as they provide valuable information about the behavior and performance of a system in the frequency domain. Researchers in this area often study techniques for analyzing, manipulating, and interpreting spectral properties to extract meaningful information from signals.