Final answer:
A UML sequence diagram illustrates the interactions between objects or components within a system.
Step-by-step explanation:
In a UML sequence diagram, the interactions between objects or components within a system are illustrated. It shows the sequence of messages exchanged between these objects or components, as well as the order in which they occur. This diagram helps visualize the flow of control and data during the execution of a particular scenario or use case.
For example, let's say we have a sequence diagram for an online shopping system. It can depict the interaction between the customer, shopping cart, and payment gateway. The diagram would show the messages being exchanged, such as 'add item to cart,' 'proceed to checkout,' and 'process payment.'
Overall, a UML sequence diagram provides a visual representation of how different objects or components collaborate to achieve a specific functionality within a system.