Cross-object formula fields
Key Takeaway
A cross-object formula reads a field on a related object by following a relationship. Write the path with relationship names, and end it with a field.
A cross-object formula is a formula that reads fields from a related object, not just from the record it sits on. For example, a formula field on Contact can show the Account Number of that contact's account. Admins use cross-object formulas to show related data, such as fields from a parent account, on the record users are viewing, in reports, and in rules.
How a cross-object formula reaches related objects
A cross-object formula spans two related objects and references merge fields on those objects. It works across lookup relationships. On the detail side of a master-detail relationship, it can also reference fields from the master (parent) object.