A CD-RW is a compact disc you can record onto more than once. RW stands for rewritable. With the right drive on a computer, you can put music or files onto it, erase them, and use the disc again — like a slower, older USB stick in disc form. It is not as tough as a USB stick: if you scratch it, it can fail. Also, not every CD player can read a CD-RW; some older music players only like ordinary pressed CDs or CD-Rs. People bought CD-RWs when they wanted a disc they could change; if they only needed to burn something once, they used a cheaper CD-R. Both are much less common now, but the contrast still matters: RW means you can do it again, R means once.