In general, information retrieval (IR) refers to the retrieval of unstructured data. Most often, it is related to TextRetrieval, i.e. the retrieval of textual documents such as newspaper and magazine articles or Web documents. Other types of retrieval include, for example, WebIR, ImageRetrieval, VideoRetrieval, andMusicRetrieval. The retrieval of information across languages is called CrossLanguageInformationRetrieval. An information retrieval system may use contextual information. This is called Information Retrieval in Context or IRiX
A more comprehensive definition of IR can be found in KeithVanRijsbergen's Information Retrieval (London: Butterworths, 1979) introductory chapter; http://www.dcs.gla.ac.uk/Keith/Chapter.1/Ch.1.html.