What are External Objects in Salesforce?
External Objects in Salesforce are the objects which are not inside Salesforce but we can access them from Salesforce and if needed we can also modify the records.
Tag external data in salesforce
How to setup External Objects in Salesforce?
For Example, you are having customer data in an MySQL server out of your Salesforce Environment then MySQL is the External Data source and the tables inside external data source are known as External Objects
