codeword

noun3

1. •
   A word or phrase (or by extension a concept) used to make a (concealed) reference to another word or concept.

   • Even the most virtuous concepts were scrutinised by governments eager to interpret them as codewords for something unwelcome. — 1993
2. •
   A string representing an encoded piece of text.

   • Bob cannot get any information out of the codeword since he doesn't know what transmission bases Alice used.
3. •
   A type of crossword puzzle where the letters of the alphabet are represented by numbers and the solver must identify them by their position and frequency.