I'm not aware that there is any + for CDs; they are either CD-R or CD-RW.
DVDs come in + and - versions, and I'm sure other contributers will be able to tell you what the differences are if you need to know.
Surface Pro 5 News - release date, UK price, features, specs
Gear VR vs. Daydream: Which delivers the best VR experience?
iPad Pro 12.9 vs Surface Pro 5
Synology invites you to visit them at Insomnia on 26th – 29th August. Book your tickets now and visit Synology.