Q: What is AVHD or AVHDX?

A: An AVHD (or AVHDX) file is essentially a differencing disk that's a child of another VHD (or VHDX) file. The "A" in AVHD stands for Automatic VHD as in Automatically Managed VHD--that is, it's managed by Hyper-V, and you shouldn't touch it.