Cyphertext is the output of an encryption system. It is typically a seemingly random series of symbols, which in fact contains the original message in some non-obvious form. If the encrypted message is transmitted over some shared medium (eg, the Internet, in smoke signals or via drums) or an eavesdroppable medium (eg, the traditional telephone system), a third party can easily see that there is some data being transferred, and can most likely determine that it is encrypted.
Using steganography the cyphertext (called stegotext) appears to be some harmless data, for example a photograph. The message is encoded into the image (in, say, the least significant bit of the data for each pixel in the image) and is not obviously visible.