An information network is a structure used for transmitting various forms and types of information. In basic structure, it consists of branches that connect certain nodes. Many scientists and researchers have dealt with the problem of defining an information network, depending on the functional organization and data transmission, and also with the classification of information networks. Information networks have a very wide application in almost all scientific disciplines. A large number of researches are carried out on the application of information networks (e.g. bisociative, deep information network, heterogeneous information network, and space information network) in the field of medicine for easier detection of diseases, drug development, etc, and other needs to support real-time communication, massive data transmission, and data processing. In accordance with the above mentioned, the aim of this paper is to offer different approaches in defining and classifying general forms of information networks and to notice their wide application in different research disciplines.