Some time back, when I started reading about OAuth, I came across Eran Hammer's Valet Key Metaphor which he used in earlier days for explaining the concept behind OAuth. It was a good analogy and a good starting point for beginners before deep diving into OAuth straight away.
Quoting Eran from his blog,
Many luxury cars today come with a valet key. It is a special key you give the parking attendant and unlike your regular key, will not allow the car to drive more than a mile or two. Some valet keys will not open the trunk, while others will block access to your onboard cell phone address book. Regardless of what restrictions the valet key imposes, the idea is very clever. You give someone limited access to your car with a special key, while using another key to unlock everything else.
This is the basic principle behind OAuth. Allow third parties to access your resources with limited privileges for a limited period of time without sharing your actual credentials.
