Full Definition: 

A message is defined as the entire package of information sent between service consumer and service (or vice versa), even if there is a logical partitioning of the message into segments or sections. For instance, if an interface expresses actions as operations or functions that take arguments, and a particular operation has two arguments, both arguments would be considered part of the same message, even though they may be logically separated within the message structure. A message also includes the concept of an attachment, in which there are several additional sections (attachments) that relate to a distinct, primary section.