18 "Also it shall be, when he sits on the throne of his kingdom, that he shall write for himself a
copy of this law in a book, from the one before the priests, the Levites.
The proper translation is in the Jewish Publication Society and the King James Version, "...that he shall write him a copy of this law in a book." This book contains, not a second law, but a repetition and expansion of the laws in the previous four books of what makes up the Pentateuch (the Torah or The five Books of Moses).
The Jewish Bible refers to this book by the third and fourth words of the Hebrew text "D'varim" or "Devarim" which mean "The Words".