What is the diffenrece between DVD+RW and DVD-RW?

[LostRabbit]

I saw one DVD burner which said it supports;

CD/CD-RW/DVD-R/DVR-RW?

I also saw domw DVD burner said:

CD/CD-RW/DVD+-R/DVR+-RW?



http://www.tigerdirect.ca/applications/SearchTools/item-details.asp?EdpNo=551788&Tab=0&NoMapp=0