yeah I know you did not ask!
You should so be blessed – well cursed at times actually – with a mind such as mine, making all these weird connections between my rumored neurons. Just be thankful that I do not share all of my random thoughts.
There are many calendars in use in the world, such as the Hebrew calendar, the Chinese calendar, and the Islamic calendar. The Julian calendar is still is used in parts of the world. There may be more that I am not aware of. Of course, the most common calendar worldwide is the Gregorian calendar, the one we here in the United States are most familiar with.
The Gregorian calendar (and Julian calendar) are divided by the time before the birth of Christ and the time after. For most of my life this has been BC which stands for Before Christ, and AD which stands for Anno Domini which is Latin for in the year of our Lord.
Quite some time ago this was decided to be cultural insensitive as there more religions than Christianity. Currently, the BC has morphed into BCE which stands for Before the Common Era, and AD has changed into CE which stands for Common Era.
Fast forward… Frequently when folks are telling s story or referencing something they will use the phrase, “this was before cell phones.” Perhaps we should now change our era nomenclature to BCP, Before Cell Phones, and ACP, After Cell Phones.
Or not.
Lagniappe: There is no zero on the Julian and Gregorian calendars because the Romans did not have a zero in their number system. This was a later import from the Arabic number system.