BC stands for "Before Christ", meaning before the birth of Jesus Christ, and AD stands for "Anno Domini" (Latin) which translated to English "Year of the Lord", meaning after the birth of Jesus Christ. So BC 100 means "a hundred years before the Birth of Jesus" and AD 100 means "a hundred years after the Birth of Jesus". Because not everybody on this planet is Christian, Catholic or any other way of believer in Jesus, the term "Common Era" is used. This is because the birth of Jesus is accepted internationally as the Common reference point for dates (in business, computers and so on). But for instance, Jews and Chinese have their own calendars. So if you don't want for some reason to involve religion on the dates being sent to somebody, is polite to use for example 100 BCE (a hundred years Before the Common Era) or 100 CE (a hundred years after the beginning of the Common Era). Note that CE and BCE are used after the year, while BC and AD are used before the year. That people usually uses them after the year don't make it right. "Circa" means "around or near" so when the happenings of an event are not known exactly you use that term. For instance, the invention of the pencil was on Circa 1564, means "that the pencil was invented around the year 1564". In this case is acepted to use the BC or AD after the year, such in "Circa 800 BC". Astaroth, Born 1972 CE

B.C. means "Before Christ" and refers to the time before Jesus Christ was born according Dionysius Exiguus (see below). 5 B.C. is 5 years before Jesus was born according to Dionysius' figuring. A.D. is an abbreviation for the Latin "Anno Domini" ("in the year of the lord", i.e. Jesus Christ) and starts with the birth of Jesus Christ. 5 A.D. is 5 years after Jesus was born according to Dionysius' figuring. C.E. is an abbreviation for "Common Era" that is used by many people who for one reason or the other do not want to use the previous system. Some are against the anno domini system for religious reasons, others are against it for historical reasons. However, 1 C.E. is equivalent as 1 A.D., and so on. B.C.E. is an abbreviation for "Before Common Era." B.C.E. works the same way as B.C., counting from C.E./A.D and moving back in time. Circa is just a useful Latin word that means "around"; as in, "My great-grandma was born circa 1880, but I don't know the exact year" It should be added that no one knows for sure when the guy we call Jesus was born. It was probably a few years off from 1 A.D. Some have argued that it was as early as 8 B.C.E. However, the Anno Domini system was created by the monk Dionysius Exiguus in 525 based on his own calculations.