OpenID is an open standard that allows users to log in to multiple websites using a single digital identity. It works by allowing users to authenticate through an identity provider of their choice rather than directly with individual service providers. This allows for a consistent user experience across different websites and services. OpenID is used by many major companies and an estimated 250 million identities have been created. It provides a more user-centric approach to digital identity that aligns with trends in the open web.