What should an administrator use as an identifier when importing and updating records from a separate system?

A Rich Text field is for formatted text display and cannot be used as a unique identifier for matching records during import.

The Salesforce Record ID is an internal, system-generated identifier that is not typically known or used by external systems for matching purposes.

An Auto-Number field automatically generates sequential numbers within Salesforce, making it unsuitable for matching records with IDs originating from an external system.

An External ID is a custom field marked as unique and external, specifically designed to store IDs from external systems, allowing Salesforce to use it for matching and updating records during import operations.