Final answer:
In cryptography, plaintext describes raw, unencrypted data, which is the original, readable message. It becomes ciphertext after applying cryptographic techniques, such as a transposition cipher where the order of characters is rearranged based on a rule or keyword.
Step-by-step explanation:
In cryptography, plaintext specifically refers to raw, unencrypted data that is the input for encryption algorithms. When using a transposition cipher, like in the Zimmerman Telegram, the plaintext would be the original message before any cryptographic operations have been applied. During the encryption process, this plaintext is rearranged according to a specific set of rules, often dictated by a keyword, resulting in what is known as ciphertext. The ciphertext is the scrambled message that hides the true meaning of the plaintext. It is only after decryption can the plaintext be recovered from the ciphertext.
To clarify the options given, encrypted data is data that has been converted from plaintext into ciphertext to prevent unauthorized access. Compressed data is data that has been reduced in size to save space or improve transmission speed, which is a completely different process from encryption. Lastly, ciphertext is the result of the encryption process, not the input.