DVD stands for “digital video disc”. Even though the word ‘video’ is in the name, a DVD can contain much more than only moving images. Audio and data are also possible. The capacity ranges from 4.7 GB (one-sided, single layer) up to 17.08 GB (two-sided, double layer). To illustrate: the latter has room for three films of 90 minutes in high quality.
The high storage capacity of the DVD is an important asset. The (re)writability as well. There are blank disks that you can buy and write yourself. Those got the name DVD-R, DVD+R or DVD-RW.