Avatar
From Halopedia, the Halo wiki
An avatar is the physical representation of an Artificial Intelligence or A.I., used as a way to better interact with humans.
While not used by all A.I.s, every "Smart" A.I. uses an avatar. This physical representation is chosen by the A.I. upon their creation and can be whatever they desire it to be, although the duty which the A.I. is to preform, combined with the human brain that was used to create it, have a great deal to do with what avatar they chose to appear as.
For more detailed information of known A.I.s that use avatars, please see the list of the Artificial Intelligence serving the UNSC.