What is the parent field for matching records in an External Lookup relationship?

In an External Lookup relationship, the matching records are primarily determined by the External ID standard field. This type of relationship is used to link a Salesforce record to a record in an external data source, ensuring there is a clear and unique association between the two. The External ID serves as a reference point, allowing Salesforce to recognize and match the records based on the specific identifier used in the external system.

Using the External ID standard field for this purpose enhances data integrity and streamlines the process of linking disparate systems, as it is designed to uniquely identify records across different platforms. This makes it essential for establishing accurate connections in External Lookup relationships.

Other options may refer to different scenarios or types of identification within Salesforce but do not serve the specific function of matching records in this context. For instance, while the Salesforce record ID is a unique identifier within Salesforce, it does not apply in the context of external records. Similarly, custom fields with unique attributes can help in various configurations but do not directly pertain to the mechanics of External Lookup relationships.