Recordable CD media (CD-R) provides for multiple session writing, which means that data can be written to disc and made accessible, then later more data can be added to the disc as long as there is unused space left on the disc.
Recordable CD media (CD) provides for multiple session writing. CD is r. Data can be written to disc. Data can be made accessible. Multiple session writing means this. Later more data can be added to the disc as long as there is unused space. This unused space is left on the disc.