[dani77]

says:

.....DVD-R (pronounced "DVD dash R") and DVD+R (pronounced "DVD plus R") are nearly identical formats. The discs look the same and are both supported by most DVD-ROM drives and DVD burners. The only difference between the formats is the way they determine the location of the laser beam on the disc. DVD-R discs use tiny marks along the grooves in the discs, called land prepits, to determine the laser position. DVD+R discs do not have land prepits, but instead measure the "wobble frequency" as the laser moves toward the outside of the disc.

The DVD-R format was developed by Pioneer and was released in the second half of 1997. DVD+R was developed by Sony and Philips and was introduced in 2002. Companies that support DVD-R include Pioneer, Toshiba, Hitachi, and Panasonic, while companies that support DVD+R include Sony, Philips, Hewlett-Packard, Ricoh, and Yamaha.

However, most of these companies now develop hybrid DVD drives that support both DVD-R and DVD+R formats. They are known as DVD±R or DVD±RW drives. When looking for media for your DVD drive, make sure it ends in "-R" if you have a DVD-R drive or "+R" if you have a DVD+R drive. If you have a DVD±R drive, you can use either format. DVD-R is still more popular than DVD+R, but since they are both widely supported, it should not matter which format you choose....."