OVF - Another Acronym to remember
At least in the virtualization world. Today almost all virtualization providers use their proprietary format to store virtual machine data on hard disks. OVF or Open Virtual Machine Format is an attempt for major players in the virtualization space to work on a common joint format for storing the information of virtual machines onto physical media.
VMware, Citrix (XenSource) and Microsoft announced working on a shared format. According to c|net, "the proposed format, called the Open Virtual Machine Format (OVF), doesn't replace the three existing standards, but instead wraps them in a standard package of XML that includes necessary information to install and configure the virtual machines."
BTW, you can read the spec here.