Junction table M:N.

Many-to-many uses a junction table: book_tags (book_id, tag_id) with two foreign keys and usually a composite PRIMARY KEY. Create books, tags, and book_tags together from an empty database.

Small example:

CREATE TABLE books (id INTEGER PRIMARY KEY, title TEXT NOT NULL);
CREATE TABLE tags (id INTEGER PRIMARY KEY, label TEXT NOT NULL);
CREATE TABLE book_tags (
  book_id INTEGER REFERENCES books(id),
  tag_id INTEGER REFERENCES tags(id),
  PRIMARY KEY (book_id, tag_id)
);