A cypher, or code, is a method used to transform information into a format that is unreadable to anyone who does not have the key to decode it. This technique is often employed in fields like cryptography to secure sensitive data, ensuring that only authorized individuals can access the original message. There are various types of cyphers, including substitution cyphers, where letters are replaced with other letters or symbols, and transposition cyphers, which rearrange the letters in a specific order. These methods have been used throughout history, from ancient civilizations to modern digital communications.