Steganography isn’t actually cryptography, but can often be used in combination with cryptography to enhance the security of the message. Steganography is the art of hiding messages. Often, sending an encrypted message would arouse suspicion, however, if the message was hidden, it would pass though without even being spotted.
Some of the most famous forms is invisible ink, and the microdot (where text is hidden in microscopic print on a page).
One of the early forms of steganography was used in ancient Greece, where a message was hidden in a wax writing tablet. Wax writing tablets were used to write messages on, the author of the message would scrape their message into the wax, however in this example, the message was written in the wood under the wax, so when the tablet was checked, it appeared blank. The message could be easily reveled when the wax was melted away at the other end.