Telecommunication is communication at a distance by technological means, particularly through electrical signals or electromagnetic waves. The word is often used in its plural form, telecommunications, because it involves many different technologies.
Early means of communicating over a distance included visual signals, such as beacons, smoke signals, semaphore telegraphs, signal flags, and optical heliographs. Other examples of pre-modern long-distance communication included audio messages such as coded drumbeats, lung-blown horns, and loud whistles. Modern technologies for long-distance communication usually involve electrical and electromagnetic technologies, such as telegraph, telephone, and teleprinter, networks, radio, microwave transmission, fiber optics, and communications satellites.
A revolution in wireless communication began in the first decade of the 20th century with the pioneering developments in radio communications by Guglielmo Marconi, who won the Nobel Prize in Physics in 1909. Other highly notable pioneering inventors and developers in the field of electrical and electronic telecommunications include Charles Wheatstone and Samuel Morse (telegraph), Alexander Graham Bell (telephone), Edwin Armstrong, and Lee de Forest (radio), as well as John Logie Baird and Philo Farnsworth (television).
The world's effective capacity to exchange information through two-way telecommunication networks grew from 281 petabytes of (optimally compressed) information in 1986, to 471 petabytes in 1993, to 2.2 (optimally compressed) exabytes in 2000, and to 65 (optimally compressed) exabytes in 2007. This is the informational equivalent of two newspaper pages per person per day in 1986, and six entire newspapers per person per day by 2007. Given this growth, telecommunications play an increasingly important role in the world economy and the global telecommunications industry was about a $4.7 trillion sector in 2012. The service revenue of the global telecommunications industry was estimated to be $1.5 trillion in 2010, corresponding to 2.4% of the world’s gross domestic product (GDP).
The word telecommunication was adapted from the French. It is a compound of the Greek prefix tele- (τηλε-), meaning "distant", and the Latin communicare, meaning "to share". The French word télécommunication was first invented in the French Grande Ecole "Telecom ParisTech" formerly known as "Ecole nationale supérieure des télécommunications" in 1904 by the French engineer and novelist Édouard Estaunié.
A number of key concepts reoccur throughout the literature on modern telecommunication systems. Some of these concepts are discussed below.