| A | B |
|---|
| B.C. | Before Christ (ex. 5000 B.C.) |
| A.D. | anno Domino - "in the year of Our Lord" (ex. 1000 A.D.) |
| B.C.E. | Before Common Era |
| C.E. | Common Era |
| Circa | around or approximately; exact date unknown, but is known to be near stated date |
| c. | abbreviation for circa; often seen with dates on timelines |
| Decade | a period of 10 years |
| Century | a period of 100 years |
| Millennium | a period of 1000 years |
| Age | a distinct period of the past |
| Era | a period of time beginning with some special event or date |
| Chronology | arranging events in the order of occurence |
