OpenID is a standard that allows you to log into many websites or services using a single identity as oppose to memorize several different username and password on different websites.
Websites that provide OpenID identity are called OpenID providers. There are many OpenID providers, and one of it is Launchpad. Launchpad users can use their Launchpad account URL as OpenID URL in order to access OpenID-supported websites or services.
For example :
The general form of Launchpad OpenID URL is: https://launchpad.net/~your_user_name.
Where I can use OpenID for authentication?
How to use Launchpad account as OpenID provider?
On website that supports OpenID, enter your Launchpad account url : https://launchpad.net/~your_user_name, replace your_user_name to your own username. Then, you will be directed to your launchpad account, enter your password and you will be automatically authenticated for the current service.
Screenshot example :
The favorable side-effect of using your Launchpad account as OpenID is that you can indirectly promote (and probably brag) about your contribution (aka karma) towards Ubuntu.