A sequence diagram is a visual representation of how different components or objects interact with each other over time in a system. It typically includes vertical lifelines representing participants, horizontal arrows showing messages exchanged between them, and activation boxes indicating the time period for each participant's activity. The order of messages reflects the chronological sequence of interactions, and activation arrows show the focus of control during each step. Additional elements like loops, conditions, and parallel interactions can be represented using combined fragments. Although the format may vary depending on the modeling language or tool, these fundamental elements provide a clear understanding of the dynamic behavior within a system.