Telegraphy is the long-distance transmission of message
A message in its most general meaning is an object of communication. It is a vessel which provides information. Yet, it can also be this information. Therefore, its meaning is dependent upon the context in which it is used; the term may apply to both the information and its form...

s via some form of signalling technology. Telegraphy requires messages to be converted to a code
A code is a rule for converting a piece of information into another form or representation , not necessarily of the same type....

 (sometimes called a "language
Formal language
A formal language is a set of words—that is, finite strings of letters, symbols, or tokens that are defined in the language. The set from which these letters are taken is the alphabet over which the language is defined. A formal language is often defined by means of a formal grammar...

") which is known to both sender and receiver. Such codes are designed according to limits of a given signalling medium
- Communication :* Medium , storage and/or transmission tools used to store and deliver information or data* Transmission medium, in physics and telecommunications, any material substance which can propagate waves or energy...


The use of smoke signals, beacon
A beacon is an intentionally conspicuous device designed to attract attention to a specific location.Beacons can also be combined with semaphoric or other indicators to provide important information, such as the status of an airport, by the colour and rotational pattern of its airport beacon, or of...

s and reflected light
A heliograph is a wireless solar telegraph that signals by flashes of sunlight reflected by a mirror. The flashes are produced by momentarily pivoting the mirror, or by interrupting the beam with a shutter...

 signals are early examples. In the 1800s, the advent of electricity
Electricity is a general term encompassing a variety of phenomena resulting from the presence and flow of electric charge. These include many easily recognizable phenomena, such as lightning, static electricity, and the flow of electrical current in an electrical wire...

 brought about the means to transmit signals via electrical telegraph
Electrical telegraph
An electrical telegraph is a telegraph that uses electrical signals, usually conveyed via telecommunication lines or radio. The electromagnetic telegraph is a device for human-to-human transmission of coded text messages....