BC and AD are acronyms that arepolitically and religiously charged artifacts of the time where religion ruled the western world. To use them today is not considered worldly nor inclusive. Further more the use of AC and BC is not representative nor based of any of humanity’s pivotal changes other than extreme religious belief.
Officially: BC and AC are results of the standardization of Julian and Gregorian calendars across Europe. The system was used for centuries across the Christian world.
AD refers to Anno Domini and translates to “Year of the Lord”