AD and BC

You sometimes see years written with AD or BC, like this:

2000 AD
450 BC

What does it mean?

AD is AFTER Jesus Christ was born.
BC is BEFORE Jesus Christ was born.

AD stands for the Latin Anno Domini meaning "In the year of Our Lord".
BC stands for Before Christ.

BC is always written after the year. AD may be written before the year or (modern style) after the year. If a year is shown without AD or BC, it is usually AD. Here are some examples going back in time:

EnglishClub was founded in 1997.
The Second World War ended in 1945.
The Gregorian calendar was introduced in 1582 AD.
Genghis Khan died in 1227 AD.
Vesuvius erupted in AD 79 and Pompeii was buried under ash.
Jesus Christ was thought to have been born in AD 1.
But he was probably born a few years earlier, around 5 BC.
Julius Caesar was assassinated in 44 BC.
In 71 BC Spartacus was defeated by the Romans.
Rome was founded in 753 BC.
The Great Pyramid was completed in Egypt more than 4,500 years ago, around 2566 BC.
Evidence of the creation and use of pottery earlier than 17,000 BC has been found in China.

You sometimes see CE and BCE instead of AD and BC. They are relatively new terms that mean the same as AD and BC.

CE stands for "Common Era" and is the same as AD.
BCE stands for "Before Common Era" and is the same as BC.

Look at these examples:

Genghis Khan died in 1227 CE. [same as 1227 AD]
Rome was founded in 753 BCE. [same as 753 BC]