OAuth is an open standard for authorization as Wikipedia puts it.
OAuth allows users to share their data or resources, hosted on a service provider, with websites or desktop or mobile apps.
Of course, if you gave your credentials (username and password) to those websites or apps, they could access your data on your behalf; but would you trust a third-party app or website to keep your credentials (your key to your digital life) safe? What if this app or website is malicious? Or simply unsecured? How many times have you read about a website getting its users credentials stolen, or keeping passwords in plain text in their databases?
OAuth is just about this; letting third-party apps or websites have a limited access (through a list ...