Question

What does common era refer to?

Answer 1

The acronyms "CE" (Common Era) and "BCE" (Before the
Common Era) both refer to the same numbering of the years
that you're accustomed to.

But you call them "AD" and "BC", and that's a problem.

"AD" stands for "Anno Domini" ... "year of our lord", numbering
years from the time of Jesus.

"BC" stands for "Before Christ" ... numbering years before
the time of Jesus.

These labels are a problem for those who do not accept the
divinity or the centrality of Jesus in the affairs of people. So
a new set of labels was needed for these sets of years.

Answer 2

The Common Era or CE refers to The Current Era or the Anno Domini (The Year of our Lord)

They are commonly interchangeable in usage since they have no difference in their system of numbering the years. The Common Era has been in use for more by mid-19th century and its usage spiked up at around the 1900s, particularly during 1980s where the usage of Common Era increased in number. Though when it comes to the official usage and as to which is which, it varies from place to place and by the scholars and laws that allow its usage.