OpenID is a standard to ensure to the world that you actually own what you claim you own online, like a blog for instance. There’€™s a lot written about it and I’€™d be lying if I said I was an expert, so if you want the full deal you should start reading at the Wikipedia page and go onwards from there.
Anyway, Technorati has added OpenID support to their members, so now you can claim your blog through them. Just login and claim it, seems simple enough. However, your blogging platform needs to support OpenID for this to work. LiveJournal and Vox does this out of the box, while WordPress and Movable Type needs plugins. There are several other platforms that support OpenID as well, beyond the blogosphere.