Acupuncture is a form of traditional Chinese medicine that inserts thin needles into specific points on the body to relieve pain and treat various medical conditions. It works by regulating the nervous system and releasing endorphins and immune cells to change brain chemistry. There are two main theories for how it works - traditional Chinese medicine views it as balancing yin and yang energies, while Western science cites effects like stimulating immunity, releasing endorphins, and impacting neurotransmitters.