codeword

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.

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

While all the cats are frolicking and singing, the aging Grizabella cat, noted once for her glamour, keeps wandering onstage and singing bits of "Memory." The other cats shun her as a pariah, an outcast. Dressed in rags, looking pathetic, it's clear that her only sin was once being "glamorous," which I think is a code word for sexual.

Even the most virtuous concepts were scrutinised by governments eager to interpret them as codewords for something unwelcome.

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.