QCOW2 stands for QEMU Copy -On- Write file. The QCOW image format is one of the disk image formats supported by the QEMU processor emulator.

QCOW2 stands for QEMU Copy -On- Write file. The QCOW image format is one of the disk image formats supported by the QEMU processor emulator. It is a representation of a fixed size block device in a file.

Source:The QCOW2 Image Format