Term for graphical representation of sound

The visual display of a sound wave can take many forms. You ask what the "graphical representation of a sound" is called, and you show an example. There are different terms for different forms of graphical representations of sound, for example sonogram, (audio)spectrogram, waveform, (audio) oscillogram. Which one to use is a technical matter.

One form is usually called a sonogram, or alternatively an (audio)spectrogram in technical usage:

A spectrogram is a time-varying spectral representation 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

This image shows Time (X axis) vs. Frequency (Y axis).

However, the picture you show in your question is different, called an (audio) oscillogram or a waveform:

Waveform means the shape and form of a signal such as a wave moving in a physical medium or an abstract representation. In many cases the medium in which the wave is being propagated does not permit a direct visual image of the form. In these cases, the term 'waveform' refers to the shape of a graph of the varying quantity against time or distance

This image, like yours, shows Time (X axis) vs. Amplitude (Y axis) and is generally called a waveform or oscillogram. Use "audio" if you want to refer specifically to the waveform of a sound as opposed to some other signal.

EDITED thanks to input from commenters.

A common word I hear used a lot in music production is Waveform.