From Halopedia, the Halo wiki
A navigation computer, sometimes abbreviated NAV computer or NAVCOM, is a device used to coordinate slipstream space jumps and plot courses or steer ships at sublight speeds. While ships often have human crews, NAV computers or AIs are essential in making the complex calculations involved in astrogation, the process of coordinating a slipspace jump. They can also control unmanned vessels, such as freighters, entirely by themselves. As they possess only a fraction of the computational capability of an AI, NAV computers are generally inexpensive. To successfully perform jumps, NAV computers require the coordinates of the intended destination and other related data, which is often in the form of a navigation database.
While the Covenant have a ban on more advanced Associated Intelligences, simple navigation AIs are in common use. Sometimes referred to as the ships' "spirits", they lack any form of sentience and are only used to control and pilot the ship, in addition to operating the intricate systems required in glassing operations and presumably make the necessary calculations for Slipspace jumps.
List of appearances