I think they are referring to burning an mp3 disk, not your normal Audio cd. Normal audio CD's can hold a maximum of either 74 mins or 80 mins approx each. mp3 disks can hold as many songs as the file sizes allows them to.

74 min cd (650 MB) can hold 650 MB of mp3 files, and of course the 80 min (700 MB) disks hold 700 MB (approx.) of mp3's.

Personally I've also burnt mp3 dvd's but I can only play them on dvd player or computer. Some players nowadays are dvd compatible.