heavily situation dependent. Autonomous region of what state, at what time, in what political context? It isn't something with a strict definition across time and space

It's hard to describe in detail but an autonomous region is afforded special rights under the Chinese constitution to set their own development plans and to set policy within the region on matters of environmental protection, the preservation of culture (think like implementing mandatory language lessons in school, restoration efforts for culturally-significant buildings and arefacts, dedicating funding to keeping cultural practices alive [one example here is that in TAR the painting of "thangka" or religious tapestries has been democratised - it used to be an artform that only monks could reasonably be trained in and resourced to do but after the reannexation of Tibet this cultural practice has been revived and it is taught today to people in Tibet to ensure that the skills and knowledge of how to produce traditional thangkas is preserved] etc.), and how the internal affairs of the region are managed including economically.

There's also special rights afforded to autonomous regions with regards to how they constitute their local government bodies and how anyone is permitted to stand for government, that all revenue generated locally is maintained within the autonomous region for the regional government to reinvest, and there's a degree of flexibility embedded into how an autonomous region applies laws that come down from a national level (this is a bit trickier to describe but if you think about EU laws on food regulations and how a country or region can apply for special provisions for ensuring that a food that is of cultural significance which would otherwise be banned under EU food regulation, they can get an exception - this is a reasonable analogy. In TAR and IMAR this might look like air quality legislation being passed by the national government that would either explicitly or implicitly prohibit the burning of wood [or dung] for fuel which would effectively outlaw people living a traditional nomadic lifestyle or specific cultural practices [think like cultural or religious celebrations that are held with bonfires] and so the autonomous government would pass exception clauses that permit for the open burning of wood for cultural reasons and for people living a traditional lifestyle. This might also look like passing exceptions on burial practices either in places like TAR and IMAR regarding religious sky burials and the maintenance of charnel grounds - things exceedingly unlikely to be legally permissible by the national government policy - or what is permitted for the burial practices specific to Muslims in XAR. Note that these are hypothetical examples and not concrete ones but so it's just a thought experiment to illustrate the point.)