Final answer:
The statement is true; a condition on a sequence diagram indicates whether a message can be processed and is used as a decision point in the flow.
Step-by-step explanation:
The statement that a condition on a sequence diagram indicates whether the message can be processed or not is True. In the context of UML sequence diagrams, a condition, often represented as a guard condition, is a boolean expression that must be true for the continuation of a flow in a sequence diagram, such as the sending of a message. For example, a condition could be used to represent a check that determines if a user is authorized before sending a message that may carry out a sensitive operation. The condition acts as a decision point where the corresponding message would only be sent if the condition evaluates to true.