What is a Track

A CD or DVD contains Tracks.  A track contains 300 or more blocks.  Tracks are located in Sessions and Sessions can contain one or more tracks.
A CD is limited to 99 tracks, a DVD+R or DVD-RW is limited to 191 tracks.  E.g. on an Audio CD every 'song' will be located in it's own track.  Data CDs mostly only contain one data track.

There are two kinds of tracks:  Audio Tracks (containing Audio sectors only).  Data Tracks (can contain M1, M2, M2F1 or M2F2 sectors)