It refers to the process of creating words that sound like the noises they represent.
However, the words created through onomatopoeia (like "buzz," "crash," or "meow") can be various parts of speech depending on their function in a sentence:
* Nouns: "The crash of thunder startled me."
* Verbs: "The bees buzzed around the flower."
* Adjectives: "The crashing waves were mesmerizing."
* Adverbs: "The car went whoosh past me."
So, while the term "onomatopoeia" is a noun, the words it describes can be various parts of speech.