c语言中typedef关键字是什么

#include <stdio.h>

#include <string.h>

typedef struct Books

{

   char  title[50];

   char  author[50];

   char  subject[100];

   int   book_id;

} Book;

int main( )

{

   Book book;

   strcpy( book.title, "C 教程");

   strcpy( book.author, "Nowcoder");

   strcpy( book.subject, "编程语言");

   book.book_id = 12345;

   printf( "书标题 : %s\n", book.title);

   printf( "书作者 : %s\n", book.author);

   printf( "书类目 : %s\n", book.subject);

   printf( "书 ID : %d\n", book.book_id);

   return 0;

}