On an optical disc like a CD or DVD disc, all data is laid out in Sessions. Sessions consist of three main components; lead-in (which stores information such as the disc TOC), a program area that contains data tracks and the lead-out. There must be at least one track in a session, and there can be as many as 99. Multisession discs contain several different sessions, and are often created to allow users to burn information to write-once media like a CD-R, several times (until capacity limit is reached).
