This looks like OVA, firmware can be bundled inside along with additional disks, networking config, machine type and so on.

So essentially a virtual appliance package

I think people these days know better than to adopt Microslop standards

this is either "embrace" or "extend", part of their business model

Looks like it means ‘Independent’ of the hypervisor used, I don’t think it’s a reference to it being an independent project. The QEMU post on this is a better read, I couldn’t tell from the GitHub what this was supposed to be. https://www.qemu.org/docs/master/system/igvm.html