Before I begin to untangle the web of participants involved in the Identity movement, I thought I should outline at the highest level what an Identity Provider is. Essentially, an Identity Provider is a company, organization, technology, etc that sits between you (the subject) and a website (the relying party). Instead of the website asking you directly for your login information (which you’ve created just for them and which they store), they ask your identity provider. You then confirm your login credentials with your Identity provider, and that provider sends an authentication token to the relying party.
This may sound like a rather complicated process for signing into a website (and it is and that is a problem I’ll address later), but this is the core technology that will enable you to be the same person across multiple websites.