The term 'change key' can be defined as a SHIFT, which is a five-letter word. It is a type of key used to encrypt and decrypt data in cryptography. It is also known as a substitution cipher, where each letter in the plaintext is replaced by another letter or symbol. The change key is used to ensure that the same message is encrypted and decrypted correctly. It is important to keep the key secure, as it is the only way to access the encrypted data.