The latest culmination of updates has been released for Windows 8.1, Windows RT 8.1, and Windows Server 2012 R2. The download, around 730MB, resolves issues, and includes performance and reliability improvements.
An Update Rollup is a batch of patches that have accumulated between major revisions of the product and it gives you the ability to deploy all the updates in one fell swoop. If you've kept up on updates or hotfixes as they were made available, you probably have most of these applied anyway, but check the KB articles to verify.
If you're installing any of the products covered by the rollup for the first time (or reinstalling in a lab), it's a great idea to apply the Update Rollup prior to using the newly installed products so you'll experience none of the annoying problems identified between revisions.
This particular rollup, contains over 50 fixes with their own associated KB numbers. You can get a quick look at everything included in the rollup by hitting this link: Fixed Issues
The rollup will show up as an Optional update in Windows Update, and subsequently your WSUS servers, but you can also obtain the rollup from the Microsoft Download Center. Download links are provided in the rollup KB article: November 2014 update rollup for Windows RT 8.1, Windows 8.1, and Windows Server 2012 R2