If you are curious as to what a Cipher is, here's the definition: - a secret or disguised way of writing; a code. - In cryptography, a cipher is an algorithm for performing encryption or decryption—a series of well-defined steps that can be followed as a procedure. An alternative, less common term is encipherment. To encipher or encode is to convert information into cipher or code. (Or TL:DR, it is a way to modify characters to "encode" or "decode" messages making a secret message to be passed along, and in order to decode a message, you typically need the "key" in order to do so since you'd have no way of knowing what pattern they used to encrypt it. ) This game basically demonstrates how strings can be modified using a few simple ciphers.