Stands for "Compact Disc Re-Writable." A CD-RW is a blank CD that can be written to by a CD burner. Unlike a CD-R (CD-Recordable), a CD-RW can be written to multiple times. The data burned on a CD-RW cannot be changed, but it can be erased. Therefore, you have to completely erase a CD-RW every time you want to change the files or add new data. While it may be somewhat inconvenient, this capability makes CD-RWs a good choice for making frequent backups. However, because CD-RWs can be erased, they don't store data reliably for as long as CD-Rs do. Therefore, you should use regular CD-Rs for long-term backups.