The time domain refers to the analysis of signals with respect to time. When the signal’s domain is space instead of time, we use the term spatial domain instead.

The frequency domain refers to the analysis of signals with respect to frequency rather than time or space. It typically shows how the signal’s energy or power is distributed across various frequencies. Phase information can also be represented in the frequency domain.

The domain terminology is related to the domain (set of inputs) of a function.

To convert a signal from the time domain to the frequency domain, you can use methods such as Fourier transform, Laplace transform, or Z-transform.