Frequency Domain
A possible representation of a time-domain signal which rather than showing how a signals amplitude changes overtime, shows how much of the signal is present among each given frequency band.
Think of sound as a combination of multiple frequencies combining at each point in time to give the sound its amplitude. Frequency domain graphs extract and partition these frequencies and their associated amplitudes into a different form.
Note: Frequency domain graphs generally only for stationary or deterministic wave forms. There're ways to get around this.