The Table of Contents (TOC) contains information about the disk and tracks. When you close the current session, the Table of Contents will be written in the Lead-In Areaaa. With an unfinished (unclosed) recording of the disk, however, the TOC cannot be written to the disk.
Every time you write to CD, you will create at least one track, which is preceded by a pre-gap and followed by a post-gap. Any session may contain one or more tracks, and the tracks within a session may be of the same or of different types (for example, a mixed-mode disk contains data and audio tracks).