A sequence diagram is a type of interaction diagram that details how operations are carried out within a system. It is used to model the interactions between objects or components in a sequence that reflects the order of operations, particularly focusing on the messages exchanged between these objects over time. The vertical axis of a sequence diagram represents time, and the horizontal axis represents the objects involved in the interaction.The purpose of a sequence diagram is to illustrate the sequence of messages or events that occur between these objects, typically in the context of a specific use case or scenario within the software system1234.

The information provided is based on standard practices in software engineering and UML (Unified Modeling Language) documentation.For further reading on sequence diagrams and their applications, you can refer to resources such as Visual Paradigm1, Creately2, IBM Developer3, and Lucidchart4.