External objects in salesforce map to data that is kept outside of your Salesforce org, much like custom objects do. To interact with the data from the external system, each external object needs to specify an external data source. For each definition of an external item, a data table is available on the external system. A table column on the external system corresponds to each field of the external item. On the Lightning Platform, Salesforce external objects enable your users to do searches and interact with external data.
