1.
onomatopoeia, sound-imitating word
A word that imitates or represents a natural sound, such as animal cries, environmental noises, or the sounds of actions. Japanese is especially rich in these.
2.
sound effect (in film, theater, etc.)
Artificially created sounds used in film, television, radio, or theater to represent real-world sounds such as footsteps, rain, or doors closing.
Usage
The full linguistic term is 擬音語 (onomatopoeia — words imitating sounds). Japanese linguistics distinguishes between 擬音語 (sound-imitating words like ザーザー for rain) and 擬態語 (manner/state words like キラキラ for sparkling). Together they are called 擬声語 or オノマトペ. The shortened form 擬音 is used colloquially for both the linguistic concept and for sound effects in media production.