lead-in - technical definition

The first part of a CD-R recording session, which starts 25 mm from the dead center of the disc and takes up 4,500 sectors. The table of contents is written into the lead-in when the session is closed. Its purpose is to allow the drive to synchronize and to hold the table of contents. If the disc is not closed, it contains the address of the next session. Contrast with lead-out.