1. Defined in dictionaries as the art of writing in ciphers or characters that are not intelligible, except to the persons who correspond with each other; cryptography (secret writing).
2. The art and science of communicating in a way that hides the existence of the communication: Steganography attempts to hide messages inside other harmless messages in such a way that third parties cannot even detect the existence of the concealed message or secrets.
3. The science of communicating in a way that hides the existence of the actual communication.

The practice of steganography involves hiding information in a wider bandwidth carrier of secrets.

Steganography covers the techniques used in digital watermarking schemes as an example from modern digital techniques, one could put the text of a message in the blank spaces in an image file.

4. In cryptography, steganography refers to not only obfuscating (encrypting) data or secrets, but hiding the fact that it even exists.
5. The art and science of hiding information by embedding secret messages within other, seemingly harmless messages: Shrinking the secret text of steganography until it is the size of a dot and then putting it in an unsuspected place; such as, the dot on top of a letter "i" in some innocuous or harmless letter.
6. Etymology: from Greek steganos, "covered, concealed, or protected" + graphein, "to write".

More details about steganography.

For other "secret" words, see: crypto-.