嗖嗖 is an onomatopoeia that mimics two distinct sounds: the sharp whizzing of something moving fast through the air (like an arrow or a car speeding by), and the sound of light laughter (like giggling or chuckling). As an onomatopoeic word, it is often used as an adverb or a standalone sound word in descriptive writing or speech. The context determines which sound is being imitated.