Ciphertext is what encryption algorithms, or ciphers, transform an original message into.
Data is said to be encrypted when a person or device lacking the cipher is unable to read it. They, or it, would need the cipher to decrypt the information.
Algorithms transform plaintext into ciphertext, and ciphertext into plaintext. These respective processes are called encryption and decryption.
“An unauthorized party to a conversation, even if they intercept our messages, would only possess ciphertext . Without the encryption algorithm and key they’d never have it in plaintext.”