By definition, cryptography is the art of writing in and solving encoded language.
Encryption is one form of cryptography.
Encrypting a message encodes it. Only recipients who know the code can read the message. Decrypting a coded message returns the message to readable form. Encryption and decryption utilize mathematical algorithms with a unique set of numbers called a key. In private key encryption, the same key used by the sender to encrypt the message is used by the recipient to decrypt the message.