The Collaborative International Dictionary of English v.0.48:

information theory \in`for*ma"tion the"o*ry\, n. (Math.,
   Telecommunications)
   The science which studies the capacity of systems to contain
   and transmit information[2], and the factors such as noise
   and channel capacity that may affect the rate or accuracy of
   information transmission and reception.
   [PJC]

WordNet (r) 3.0 (2006):

information theory
    n 1: (computer science) a statistical theory dealing with the
         limits and efficiency of information processing

Moby Thesaurus II by Grady Ward, 1.0:

42 Moby Thesaurus words for "information theory":
   EDP, automatic electronics, autonetics, bionics, bit, channel,
   circuit analysis, communication engineering,
   communication explosion, communication technology,
   communication theory, communications, communications engineer,
   communications industry, communications medium,
   communications network, cybernetics, data retrieval, data storage,
   decoding, electrical communication, electronic communication,
   electronic communications, electronic data processing, encoding,
   entropy, information explosion, media, noise, radio control,
   radiocommunication, redundancy, servo engineering, servomechanics,
   signal, signaling, system engineering, systems analysis,
   systems planning, telecommunication, wire communication,
   wireless communication