An onomatopoeia is a word that phonetically imitates, resembles or suggests the source of the sound that it describes. Onomatopoeia (as an uncountable noun) refers to the property of such words. Common occurrences of onomatopoeias include animal noises such as "oink", "miaow" (or "meow"), "roar" or "chirp". I don't know if you read comics but sometimes someone will hit something and it will say "BANG" it basically a sound.