In algorithmic information theory (a subfield of computer science and mathematics), the Kolmogorov complexity of an Object, such as a piece of text, is the length of a shortest computer program (in a predetermined programming language) that produces the object as output. It is a measure of the computational resources needed to specify the object, and is also known as algorithmic complexity, Solomonoff–Kolmogorov–Chaitin complexity, program-size complexity, descriptive complexity, or algorithmic entropy. It is named after Andrey Kolmogorov, who first published on the subject in 1963 and is a generalization of classical information theory. wikipedia 
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LI, Ming and VITÁNYI, P. M. B., 1997. An introduction to Kolmogorov complexity and its applications. 2nd ed. New York: Springer. Graduate texts in computer science. ISBN 978-0-387-94868-3