"B.C." stands for "Before Christ," a designation used to label years in the Gregorian calendar system. This system counts years backward from the estimated birth year of Jesus Christ, with 1 B.C. being the year immediately before 1 A.D. The B.C. era is commonly used in historical contexts to refer to events that occurred before the start of the Common Era. The B.C. designation is often paired with "A.D.," which stands for "Anno Domini," meaning "in the year of our Lord." Together, these terms help historians and scholars organize and reference historical timelines. Other systems, such as BCE (Before Common Era) and CE (Common Era), are also used to provide a secular alternative.