What is an OpenID?
OpenID is a mechanism for authenticating individuals using a decentralized approach. Please review the link for more information, as I would almost certainly not give a clear explanation.
For this site, however, it means that I don’t actually store any database of users to authenticate against for submitting comments. You can log in using any (as far as I know) valid OpenID that follows the standard. You may already have an OpenID, since various services are already configured to serve as an OpenID provider.