I have seen on websites that you can buy blank DVD media called DVD-Ram for drives that are capable of burning it. But what is DVD-Ram and what is the difference between it and DVD-R and +R
Well, essentially it is a flavour of rewritable DVD like DVD+RW and DVD-RW, but with some additional features. And beware, not all burners/readers/standalones support it.
You’ll find tons of info here and on the net, but of course a very good start is the wikipedia.