What are CD-R and CD-RW? What is 'multi-session' burning?

A CD-R is a blank CD on which you can record, but not erase and re-write. A CD-RW is a little more expensive, but data on it can be erased and rewritten.

A CD-R is a blank CD on which you can record, but not erase and re-write. A CD-RW is a little more expensive, but data on it can be erased and rewritten.

Nothing stops you from recording on a CD-R, and then adding more data later over several sessions until it fills to the brim. This is called 'multi-session' burning. All CD-burning software provide this feature.