Microsoft's product releases and varying editions of those product releases can most times be a convoluted mess. When a customer starts to research which product edition will meet their needs, they want to ensure that business requirements are met exactly, that the selection provides a little growth room, but that's also not overkill in features and cost. Microsoft doesn't make it very easy to locate this information.
To help, Microsoft has released a fantastic, single-page resource that lists out the different Windows Server 2012 R2 products and editions and compares them. It covers Windows Server 2012 R2 Datacenter, Windows Server 2012 R2 Standard, Windows Server 2012 R2 Essentials, Windows Server 2012 R2 Foundation, Microsoft Hyper-V Server 2012 R2, Windows Storage Server 2012 R2 Standard, and Windows Storage Server 2012 R2 Workgroup.
Whew! I bet many of you had no idea there were that many editions of Windows Server 2012 R2. It does make you want to shake your head.
Despite, in my opinion, Microsoft offering simply too many different server products, it is nice to see them all listed in a comparison matrix and separated out by limits, roles, and features for easy review. It's not fancy, it looks like someone keyed everything into Excel and then used the "Print to PDF" option, but it's definitely useful.
You can download it (PDF format) here: Windows Server 2012 R2 Products and Editions Comparison