Message data is the application data or the contents of the message body. For example, if an application sends a list of customer names to another application, the customer names comprise the message data component of the message. The content and format of the message data is defined by the application that uses the message queue. WebSphere MQ does not enforce any structure on the content and format of the message data. In PowerCenter, MQSeries source definitions and dynamic MQSeries target definitions contain a message data field.