It is when a word imitates the sound it is trying to represent.
Moo- to imitate the sound a cow makes
Pow- to imitate the sound a punch makes
Ding- to imitate the sound a bell makes
Etc.
It is commonly spelled onomatopoeia.
Onomatopoeia is a literary device in which the word imitates the sound it represents, like "buzz" or "sizzle." It is commonly used in poetry and storytelling to create vivid images and sensory experiences for the reader.