App registrations : Since, we all know that the Azure portal is the best place to register your organization's applications. App registrations helps the administrator to decides who can access that particular app. Mostly, that application is used by own tenant only, but there were other options available like Multi tenant and MSA support. Basically, App registrations shows all the applications present in your tenant that have been registered.
Enterprise Application : In this Enterprise application module, Global admins can by default able to see external applications that are registered by other companies in AAD(Azure AD) gallery. You can also able to view app registration inside enterprise application. So, basically enterprise application can shows all the global apps which belongs to other tenants.
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