Question

What does anno domini mean

Answer 1

It means "year of our lord" in Latin, meaning the number of years since Jesus.
The years before the AD ones are labeled 'BC', for "Before Christ".

Both of those labels are the reasons why many people, especially
non-Christians, such as for example Jews and Muslims, prefer to
label the years as 'BCE' and 'CE', meaning "Before the Common Era"
and "Common Era".