Auralism is a sexual fetish
defined as sexual arousal or excitment caused by sound, to be compared with voyeurism
. This sound might be music, a voice, the actual sounds of sex itself, or other sounds, and may include enjoyment from listening to others having sex. As with most fetishes, in some cases it is simply a small additional turn-on, and in others it is a requirement to sexual gratification.
Since the sound of her lover's voice in her ear made her groan with pleasure and get weak in the knees, he defined the word auralism just to describe her fetish, which until then, didn't seem to have a name.