Google Blog Search is a specialized search engine for blogs that used to be featured in Google's navigation menu. Google no longer links to the service and one of the only ways to use it was to go to blogsearch.google.com. Now Google redirects the URL to the Google homepage.
You can still use this URL: https://www.google.com/?tbm=blg, but this is just a workaround and Google will eventually remove it.
Search Engine Land has incorrectly reported that Google Blog Search is now inside Google News. Actually Google News has a search filter that only shows the blogs from the Google News index. Obviously, not all the blogs are indexed by Google News and Google News only shows results from the past 30 days.