The "A-series" refers to a classification of time proposed by philosopher J.M.E. McTaggart in his work on the nature of time. In this framework, events are categorized based on their temporal properties, such as past, present, and future. The A-series emphasizes the dynamic nature of time, where events change their status as they move from the future to the present and then to the past. In contrast to the A-series, the B-series presents a static view of time, where events are ordered by their relations to one another without the changing properties of pastness, presentness, and futurity. The A-series has sparked significant philosophical debate regarding the nature of time and our understanding of reality.