cleartext vs plain text

cleartext

noun
  • The unencrypted form of an encrypted text; plain text 

plain text

noun
  • Text or any data that is to be encrypted (as opposed to ciphertext). 

  • Data which consists only of human-readable text, as opposed to machine-readable binary data or formatting markup. 

adj
  • Consisting only of plain text. 

How often have the words cleartext and plain text occurred in a corpus of books? (source: Google Ngram Viewer )