many2many fields are similar to many2one (i.e. they create a new database relationship), except that multiple records can be selected.
These are sometimes displayed as ‘tags’, using the
many2many_tags widget, as shown on Contacts:
Multiple tags can be selected for a vendor (or other contact).
They can be displayed using checkboxes using the
many2many_checkboxes widget (as in Account Journal payment methods):
Multiple payment methods can be selected for a journal.
It’s also possible to display a list (similar to one2many) using the
The “Send and Print” invoice wizard has examples of two other many2many ‘widgets’:
many2many_tags_email(for email recipients)
Other widgets include: