...dvd-rw?

Only difference is that a dvd-rw is rewritable, meaning you can go back and burn something else on or over the current data.

DVD-R is a non-rewriteable format, while DVD-RW is a rewriteable format.

www.videohelp.com

rw is re-writable while plain R is write once and then that is it.

The "r" in "dvd-r" stands for "recordable". The "rw" in "dvd-rw" stands for "rewritable". DVD-R discs are typically writable (recordable) only once. Each time you write to a DVD-R (each time being called a "session"), you add more information to the disc until it is full. Once the DVD-R is full, you can no longer add information to the disc. DVD-RW allows you to do the same, but you can also "erase" information from the DVD-RW and keep using it over and over.

www.cdrfaq.org

DVD-RW can be re-written, but DVD-R can't.That is to say, you can re-use your DVD-RW by "erasing" or "formatting" it. But DVD-R can only be used once under normal cicumstances, assuming you have already "finalized" the disc.