In Unified Modeling Language (UML) sequence diagrams, a stop node represents the destruction of an instance in an interaction.
As the following figure illustrates, a stop node appears at the bottom of a lifeline and is indicated by a destruction marker, which is denoted as an X.
When you create a destroy message, a stop node is created automatically. However, you can manually create a stop node on a lifeline to represent the destruction of an interaction instance at a specific position.