Steganography is the art and practice of communicating using hidden messages, often disguised within something else where one would not expect a message to be contained in. Generally steganographic messages will appear ordinary at first glance: an image of a cat, a grocery list, an article or poem, etc. Hidden within these ordinary writings or objects (in steganographic terms, the covertext) is the hidden message.
The main difference between steganography and cryptography and encryption is that the messages do not attract attention to themselves. Steganographic communications hide often in plain sight, whereas encrypted communications are, while undecipherable, very obvious of the fact they are sending secrets.
A common example of steganography is often related to digital media files, as they are an excellent way to store messages due to their large size and general inconspicuous nature. For example, one could turn every 100th pixel in an image file to a color that corresponds with a letter of the alphabet. While the image itself would not appear overly distorted (perhaps slightly corrupted at worst) one could easily take the image and find the message.
Steganography relies on not being seen or inspected – when it is detected there is very little protection on it’s own. Combine steganography and cryptography however, and you have a very secure method of communication – Hidden and encrypted messages.