The 'karaoke version' of a song, usually refers to music that has been recorded without vocals. They are produced in the style of the original artist and in the same key. Genuine karaoke song versions do not have any original artist vocals whatsoever. The most common form of Karaoke file are:
MP3+G is a relatively new karaoke file format that was created to allow CD+G karaoke files to be played from a PC. MP3+G contains an MP3 audio file, and a raw CDG file which contains the lyrics. It is common for an MP3+G song to be zipped up as a .zip for ease of file transfer.
CD+G is an older version of karaoke file. It is based on the compact disc standard and adds a low-resolution graphics alongside the audio data on the disc when played on a compatible device.