What exactly is OAuth (Open Authorization)?

Question

What exactly is OAuth (Open Authorization)?

I have gleaned some information from

• OAuth
• Twitter Tutorial: What is OAuth And What It Means To Y

Answer 1

OAuth happened when we sign up SO account with Facebook/ Google button.

1. Application (SO) redirecting user to the provider's authorization URL. ( Displaying a web page asking the user if he or she wishes to grant the application access to read and update their data).
2. User agree to grant the application process.
3. Service provider redirects user back to application (SO), passing authorization code as parameter.
4. SO exchanges the code for an access grant.

Source : OAuth1 service providers