In 23rd century Stark movie stars still exist but have for the most part been replaced by simple recordings of their image, or "avatars". They are designed to be completely faithful representation of the actor concerned, which are then used in lieu of the actor himself on set.
The 'Stars Recycled' news article on the FACT machine mentions 'avatar extraction'. Given the level of technology in TLJ, it is possible that the avatar is generated using holographic technology, based on physical scans and voice prints. As all the director has to do is 'instruct' the avatar to act, it probably only has a modicum of artificial intelligence.
The term avatar is known to us from Indian mythology, and indicates hypostases of gods (ie. Krishna is an avatar of Vishnu).
In the late 20th and 21st century "avatar" is used to designate a person's pictoral representation in a virtual world, such as the internet or an RPG. Usually they can be customised to the individual's taste.