External objects are similar to custom objects, except that they map to data that’s stored outside your Salesforce org. External objects enable your users and the Lightning Platform to search and interact with the external data. Note. Each org can have up to 100 external objects.
External Object is a kind of virtual object which does not exist in your Org. It is a custom object like other custom objects we can use in visualforce, apex, soql, sosl, and custom tabs.