Enterprise Applications vs App Registrations

Enterprise Application

Enterprise application is also known as a Service Principal.

It is shown as a blue grid with a green world icon in the corner. In the search box it is shown as a Service Principal, but if you click through to the resource, it is an Enterprise Application. 

Clicking on the Service Principal (the bottom one above), it shows you the Enterprise Application resource.

App Registration

If you click on the Application entry in the search box

It takes you to the App Registration.

It is the Application Registration client secret that the application uses to prove its identity when requesting a token. Also can be referred to as application password. This needs periodic renewal.

Additional Information

https://stackoverflow.com/questions/65922566/what-are-the-differences-between-service-principal-and-app-registration