According to SuccessfulBlogging.com Technorati Ranking relates to the number of sources that point to your blog relative to other blogs. The more sources referencing your blog, the higher the Technorati ranking. The Technorati Ranking for a blog is displaying in URL Search results, Blog search results, and is displayed in the account profile for all claimed blogs.
Technorati Authority is the number of blogs linking to a website in the last six months. The higher the number, the more Technorati Authority the blog has.
In a nutshell- the more blogs that link you your blog the higher your authority is.