db.inventory.remove({ type: 'Book'});

In case of delete by default multi is true, no need to mention

If you don't want delete multiple document, then your query will be db.inventory.remove({ type: 'Book'},{multi: false});

Seems that's wrong , The doc says something different.

db.collection.remove( <query>, <justOne> )

justOne (boolean) Optional.

To limit the deletion to just one document, set to true. Omit to use the default value of false and delete all documents matching the deletion criteria.