NRG is a CD/DVD image file format used by Nero Burning Rom tool. NRG image files contain backup copy of a disc or data to be burned into an optical disc. Disc images can also store various typed of data and can be mounted on the system as a virtual disk and used like a normal disk.

NRG disk image files are created as a result of block-by-block copy process of original data, not by copying files and folders. NRG is a 1:1 copy of data.