This relationship involves at least three entities ( table occurrences ) all lined up in a row. It starts off when one record in an entity ( table occurrence ) is related to many records in another entity ( table occurrence ). Each record in that entity ( table occurrence ) is in turn related to one record in another entity ( table occurrence ). Here is a classic example of how this works in FileMaker.
We have one invoice record that has many sold products on it. Each sold product is a record in the middle database entity ( table occurrence ). Each one of those sold items is related to on product in an inventory entity ( table occurrence ).
So the middle or join table occurrence will have a number of records with an invoice id and a product id. The one invoice can total a number of sold products and product can be sold many times.
There are a lot of variations of the middle /join entity ( table occurrence ) and you can have multiple middle entities ( table occurrences ). That is to say one relationship can depend on another ... that depends on another relationship. The relationship can even tunnel through the join entity ( table occurrence ).
For example, a table occurrence called products might be able to see a minimum or maximum value through the join file to the invoice file.