Complex sentence: 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.
Split into simpler sentences: Recordable CD media (CD-R) provides for multiple session writing. This 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.