Frequency domain refers to the mathematical analysis of signals and functions based on frequency instead of time. The representation is particularly essential when it comes to analyzing linear systems. This is because it shows the amount of signal is within a given frequency band over a range of frequencies.
The frequency-domain analysis is a tool of utmost importance in applications processing signals. This is because it contains phase shift information that is included in each frequency component if the original time signal, together with its individual frequency components, is to be recovered. Areas that use this type of domain analysis include remote sensing, geology and image processing.