The phrase "what is the books" appears to be grammatically incorrect. However, if we assume that the intended phrase is "what are the books," then possible synonyms include "which titles," "which volumes," "what literature," "what publications," "what reading material," and "what written works." Each of these synonyms could be used to refer to a collection of books or specific titles that the speaker is either referring to or asking about. By using different synonyms, speakers can vary their language and better articulate their thoughts or questions about books.