Nanites are robotic devices used inside the body primarily for medical purposes. Most people in the Pax Imperium have nanites in their blood at all times monitoring their body if not intervening to improve their health in some way or another.
Emergency medical nanites (EMNs) are a special class of nanite injected when a medical need arises. They are designed to perform life saving functions, such as coagulation and stimulating the adrenal gland.
Nanites can also be used to take over parts of the brain including the visual and auditory cortices causing the victim to hallucinate. When nanites are used in this way it is called a mind hack.