the relationship field;

invert direction: ACF Relationship doesn't support natively Many-to-Many relations, but our widget can simulate and resolve it;
​ EXAMPLE: if you associated the Authors to the Books with an ACF Field stored in Books CPT, normally you can only list the Authors in Books single page.
With this Inverted direction setting you will be able to list all Books associated to Authors in the Authors single page.

number of posts to display (-1 means "all");

order by Post ID | Post Author | Title | Date | Last Modified Date | Parent ID | Random | Comment Count | Menu Order | Meta Value NUM | Meta Value DATE. If you select "Meta Value" you must choose the Meta Field;

order ascending or descending.