When viewing a list of records e..g opportunities, within a form there is a view option called “all affiliated records”.
To explain this imagine we are working with an Account record, ABC Ltd that has a number of contacts.
The include option, This record only, shows only opportunities that are directly linked to the record (ABC Ltd).
The include option, Related “Regarding” Records, shows opportunities that are linked to records that are related to ABC Ltd For example, opportunities linked to any of the contact records that are parented by ABC Ltd will be shown as well as ones linked directly to ABC Ltd.
The include option, All affiliated Records, shows only the opportunities where the record (ABC Ltd) is linked via Relationships (see left hand navigation of the Opportunity form). Opportunities linked to ABC Ltd or its contacts are not shown.