Data transmissionData transmission is, very generally speaking, the conscious act of moving any kind of information from one space to another. Historically this could be done by courier, a chain of bonfires or semaphores, and later by Morse code over copper wires.
In recent computer terms, it means sending a stream of bytes from one location to another using any number of technologies to do so. Among them are copper wire, optical fibre, radio-link, laser, radio or infra-red light.
A related concept to data transmission is the data transmission protocol used to make the data transfer legible. Current protocols favour packet based communication.