Which of the following is not a type of message in sequence diagrams?

In sequence diagrams, messages represent the interactions between objects over time, and there are specific types of messages that are commonly recognized within UML (Unified Modeling Language).

Synchronous messages are those where the caller waits for the callee to process the message and return a response before proceeding. This is a fundamental aspect of many interactions in object-oriented design.

Asynchronous messages, on the other hand, allow the caller to continue processing without waiting for a response from the callee. This type of message indicates a more flexible interaction where the two objects do not need to coordinate their timing directly.

Create messages are specific to the context of object creation, indicating that a message is sent to create a new instance of an object. This type of message is also recognized as a valid representation of interactions in sequence diagrams.

However, a delayed message is not a standard type recognized in UML sequence diagrams. There are ways to represent delays, but they do not have a distinct categorization as a message type. Instead, delays can be inferred through the timing of the sequence and are often indicated with timing constraints or by using specific lifelines. The lack of a defined "delayed message" type signifies that it does not belong in the usual classification of message types within this modeling context.