BC stands for "Before Christ." It is referring to a time period before Christ was born, according to the Christian churches. However, people with more secular beliefs will refer to this time as "Before Common Era," or "BCE."
Years during this time can be a bit confusing, since it's the opposite of how we read years in AD. For example, if we say 2012 AD, we know that they are referring to 2012 years after the birth of Christ. Therefore, the date 2000 AD would be before 2012.
However, when referring to 2012 BC, you are talking 2012 years before the birth of Christ. Therefore 2000 BC would be after 2012 BC. Similarly, if you were talking about 1000 BC, it would be before 2012 BC.
