Cryptology is the science that studies secret communication.
A code is a system of symbols, letters, words, or signals that are used instead of words and numbers to send messages or store information. A code is used to keep the message short or to keep it secret.
Codes and ciphers are forms of secret communication. A code replaces words, phrases, or sentences with groups of letters or numbers, while a cipher rearranges letters or uses substitutes to disguise the message.
This process is called encryption or enciphering. The science that studies such secret communication is called cryptology.