Message Message Medium-power talker Message in its most general meaning is the object of Communication. Depending on the context, the term may apply to both the Information contents and its actual presentation.

In the Communications discipline, a message is Information which is sent from a source to a Receiver. Some common definitions include:

Any Thought or IDEA expressed briefly in a plain or secret Language, prepared in a form suitable for transmission by any means of communication.
An arbitrary amount of Information whose beginning and end are defined or implied.
Record information, a Stream of Data expressed in plain or encrypted language (Notation) and prepared in a Format specified for intended transmission by a telecommunications System.

In the Actor model a message is similarly an Actor itself that is sent asynchronously from one Actor to another.

In languages such as Smalltalk-80 and Objective-C an instance of a class method is called (confusingly) a message.

History of messaging

Smoke signals - Ancient (short distance only)
Wind-power shipping (hence the name) "In 1800, it took 2 years to send a message from London to Calcutta. You wrote a physical letter and entrusted it to a wind-powered ship that sailed down the western coasts of Europe and Africa, around the Cape of Good Hope, back up the eastern coast of Africa, across the Arabian Sea, etc. -- with, presumably, stops in just about every port (yes, they had multi-hop message transports back then)."
Semaphore - Limited use
Telegraph - (late 19th century)
Telephone - (late 19th century-early 20th century)
Steamshipping "By 1914, it took 1 month to send a message from London to Calcutta. The Suez Canal had opened, and steamships powered their way through the Mediterranean to the Red Sea, and thence to India. Big improvement."[1]
Radio, (early 20th century)
Television - (mid 20th century)
Airmail (1950s or 1960s?) ~ 1 week.
Overnight mail - became popular and affordable in the 1980s, made the international messaging only two days.
Electronic mail (~1994) - delivery times of 10 minutes, based on number of hops, frequency of manual retrieval, etc.
Instant messaging - Message travels at average 100 milliseconds, almost always less than a second. Often shorted to "IM", sometimes in combination with the type of messenger (YIM is yahoo instant messenger).

References

"Brief history" section adapted from Peter Saint-Andre "The Need For Speed"
Department of Defense Dictionary of Military and Associated Terms
Federal Standard 1037C