DVD stands for 'digital versatile disc' and can be in the form of a DVD video disc, a DVDrom data disc, or both. Standard capacity discs are 1hr best quality video, or 4.5 gigabytes of data. (ie 1hr of video takes up 4.5 gigabytes on the disc). The video quality can be 'dropped' to increase the disc capacity. (2hrs on a disc is still very good quality).
There are also Dual-Layer disc available and essentially doubles the capacity of the disc.