Concealed writing or information; producing and concealing secret messages in computer files that can only be detected by special software.
Virgilius, Bishop of Saltzburg, having asserted that there existed antipodes, the Archbishop of Mentz declared him a heretic; and the Abbot Trithemius, who was fond of improving steganography or the art of secret writing, having published several curious works on this subject, they were condemned, as works full of diabolical mysteries; and Frederic II., Elector Palatine, ordered Trithemius's original work, which was in his library, to be publicly burnt.
Isaac D'Israeli, Curiosities of Literature. Amazon
Other security-related applications include information-hiding and data steganography - the hiding of data inside other data - for commercial products, as well as those related to national security.
There's nothing new about steganography, in principle at least. Herodotus tells the tale of Histiaeus who, in the sixth century BC, shaved the head of his most trusted slave, tattooed a message on his scalp and let his hair regrow.
Ian Sample, The Guardian, 11 August 2005. Guardian
Shortly after Sept. 11, questions swirled around steganography, the age-old technique of hiding one piece of information within another. A digital image of a sailboat, for instance, might also invisibly hold a communiqué, a map or some other hidden data. A digital song file might contain blueprints for a desired target.