Who is the undercover library? Another word bookstore. There are many synonyms for library, and the library bookstore is one of them. The difference between a library and a bookstore is that books in the library are not for sale, but books can be bought in the bookstore. "Who is Undercover" is a game to compete for language expression ability, knowledge and imagination. Among the n(n is greater than or equal to 3) people present, (n-x)(x is the number of undercover, optional) people get the same word, and the remaining x people get another word related to it.