According to their About page, Technorati currently tracks over 80 million blogs. Every time one of those blogs writes something new, they send a ping to Technorati, telling them they've posted something new along with some tags (What are tags?) and basic information about the post. Technorati immediately adds that post to every search for any of those tags.
Basically, this enables Technorati to search the web, specifically the blogosphere, in real time and makes it an invaluable resource for up-to-the-minute information online.
Please see Mahalo's Technorati search result page for more information.
