An information source is a sequence of random variables ranging over a finite alphabet
are reachable, in one step, from a common prior state.
Unifilar sources are notable in that many of their properties are far more easily analyzed, as compared to the general case.
Markov sources are commonly used in communication theory, as a model of a transmitter.
Markov sources also occur in natural language processing, where they are used to represent hidden meaning in a text.