A spectrogram is a time-varying spectral representation (forming an image) that shows how the spectral density of a signal varies with time.
Also known as spectral waterfalls, sonograms, voiceprints, or voicegrams, spectrograms are used to identify phonetic sounds, to analyse the cries of animals; they were also used in many other fields including music, sonar/radar, speech processing, seismology, etc. The instrument that generates a spectrogram is called a spectrograph and is equivalent to a sonograph.
Source: Wikipedia – Spectrogram
