Описание тега belongs-to
This is a master-detail relationship where one item "belongs_to" another and has a foreign key to maintain the relationship.
A master record has many detail records.
For example if we have buildings and rooms we can say that one building has_many rooms.
In a database, with tables/models, this relationship implies that rooms will have a foreign key for which building they belong to and thus the relationship will be belongs_to.