Communication is the transfer of information from a person to another or from a place to another. It usually means the transmission of words, sounds, picture, or data in the form of electronic signals or impulses.
Communications are of two types:
Analogue communication refers to a linear and continuous change of the signal. Digital communication consists in separated steps. The digital representation uses numbers comprised in a series of 1s and 0s.
In the past there was the analog communication because the digital one didn't exist. Digital communication involves a series of electronic pulses. Original radio telegraph and telephone system were in the past analogue but today they are all digital. This change has been possible thanks to the invention of the transistor in the middle of 20th century. The advantage of digital communication are: speed, size, power, and low consumption compared with traditional analogue means.