Is it 2010 AD or 2010 CE?
There are many different calendars around the world (e.g. Hindu, Hebrew, Indian, Islamic, Chinese, Buddhist, Bahai). Usually they have a religious origin.
All have different dates for the current year (e.g. 2010 AD = 5112 Hindu, 5771 Hebrew, 1932 Indian, 2002 Ethiopian).
The Christian calendar is currently understood and widely used throughout the world, however the association with a specific religion is difficult for some atheists and some people of other faiths. It is becoming more frequent to see the letters CE and BCE used instead of A.D. and B.C.
A.D. = Anno Domini = CE = Common Era (also, very rarely, = E.V. or V.E. = Era Vulgaris or Vulgar Era)
2010 AD = 2010 CE
B.C. = Before Christ = BCE = Before Common Era
1000 BC = 1000 BCE
"Vulgar Era" has been in (occasional) academic use in England since 1716
"Common Era" is noted in an encyclopaedia dated 1908
For archaeology, geology and pre-history studies, other abbreviations are often used -
B.P. = Before Present = Years before 1950 AD/CE
5000 BP = 3050 BC = 3050 BCE
Y.A. = Years Ago = Years before today
B.P. - 1950 is the "Present" because that was the year that radiocarbon dating was accepted, and therefore became the base year.
Y.A. - this is not much use in a book unless reference is made to the date of publication.
Further reading -