This article explains the differences between DVD-ROM, DVD-RAM, and DVD+RW.

DVD-ROM, as its name implies, is a "read-only memory" format. Your computer can read a disc's contents, but it cannot save data to one.

DVD-RAM (DVD random-access memory) and DVD+RW (DVD rewritable) are both rewritable mediums. DVD+RW is a rewritable format that has not yet been standardized. DVD-RAM is a rewritable DVD standard that has been finalized and published by the DVD Forum, a group of 10 industry-leading corporations.