Controlling fields for picklist dependencies
Key Takeaway
A controlling field's value decides which values a dependent picklist offers on the same record. A controlling field can be a standard picklist, a custom picklist, or a checkbox. A dependent picklist is a custom picklist or a multi-select picklist.
A dependency links two fields on the same record, so a user's choice in one field filters the choices in the other. Admins set up this filtering in Object Manager under "Field Dependencies" to help users enter accurate and consistent data.
Controlling fields and dependent picklists
A dependent picklist is a custom picklist or multi-select picklist whose valid values depend on the value of another field. That other field is the controlling field, and it must be on the same record as the dependent picklist.
For example, imagine a custom Reason picklist on opportunities that depends on Stage, so Stage is the controlling field. When the Stage is Closed Won, Reason allows Superior features or Lower price. When the Stage is Closed Lost, Reason allows Inferior features, Higher price, or Company viability.