What Is Apps Using Apple ID: In System Pref Apple ID, Password & Security About?

In Apple ID > left menu Password & Security > Apps Using Apple ID: section. When I recently updated my Apple ID password a notice popped up showing that I allow two apps (DropBox and PBS Video) to us my Apple ID. I’d like to learn more about this. If this has already been covered I’d appreciate the link/s or keywords for a search.
The fact that I “unknowingly, to the best of my memory” allow apps to use my Apple ID seems a security concern. Mainly because of my ignorance on the subject.
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Pat Maxim