Related lists and object tabs for relationships
Key Takeaway
A lookup or master-detail field can produce a related list. You name the list with the Related List Label on that field. You choose its fields and buttons on the page layout of the object that displays it.
A related list shows records from a related object on another record's page. App builders control what each related list is called, which fields and buttons it shows, and whether the related object also gets its own tab. These choices shape how users find and work with related records, especially detail records and the junction records in a many-to-many relationship.
Where a related list comes from
Both lookup and master-detail fields can produce a related list.
For example, an account record shows its contacts on the Related tab, along with a button to quickly add a contact.
In a master-detail relationship, you always create the relationship field on the detail object, and the related list shows on the master.
For example, imagine you create a master-detail field on Favorite that points to Property. Favorites then appear in the Related tab of each Property record, and users can click "New" there to add a favorite.