What is the difference between Windows Server 2012 Standard edition and Windows Server 2012 Datacenter edition?

Both Standard and Datacenter editions provide the same set of features; the only thing that differentiates the editions is the number of Virtual Machines (VMs). A Standard edition license will entitle you to run up to two VMs on up to two processors (subject to the VM use rights outlined in the Product Use Rights document). A Datacenter edition license will entitle you to run an unlimited number of VMs on up to two processors.