Q: What is "OAuth"?  

Correct option:
An open standard that allows users to share personal resources stored on a site with another site, without having to share their credentials.

Explanation:
OAuth (Open Authorization) is an open standard for access delegation. It allows users to grant third-party applications limited access to their resources (like data) on another service without sharing their credentials (such as username and password). For example, a user might allow an application to access their Google contacts, but the application would not have access to their Google password. OAuth allows this secure delegation of access through access tokens, rather than exposing the user's credentials.