There seems to be a bit of confusion to what the abbreviation "CDG" actually means. Some search phrases often used to find this site include "download CDG files", "burn CDG files", "create CDG files", etc..
The abbreviation CDG, which is actually a shortened version of CD+G, stands for "Compact Disc plus Graphics" which is the most popular type of karaoke disc. These discs contain standard audio sound tracks that have graphics (images and lyrics) written in the normally unused "subchannel" portion of the tracks. CD+G discs do not contain video.
If you would view the contents of a karaoke CDG disc, in Windows explorer for example, you would find that it contains files of the .cda extension just like any standard audio disc. The .cda extension is actually a shortcut as opposed to an actual file type extension. If you play a CDG disc in a standard CD player you will be able to hear the audio. You must have a karaoke (CDG) player in order to display the graphics on a monitor or television screen.
The .cdg file extension is used for a variety of purposes. This leads to the confusion of what a CDG file is. The MP3+G™ format uses a .cdg extension for the graphic file of the file pair that makes up each MP3+G™ song track. Some karaoke software applications create BIN files but give them the .cdg extension. Some midi karaoke files have been given a .cdg extension.
The song tracks that are ripped from a CD+G disc are not CDG files. They are typically ripped to the MP3+G™ format (compressed format for playing with software players from a hard drive) or BIN files (full sized files used to make copies of CDG discs or to create custom compilation discs). You will find a large selection of software for working with karaoke discs at the Karaoke SoftShop.