This function is used to exclude audience which can be needed to prevent the Follow (tracking) camera to detect other people in the room (placed at the bottom area of the shot, like students in that picture below), therefore the software will only be following the teacher (the only one out of the audience exclusion zone)

In the Audience Exclusion page (web GUI: Teacher Tracker > Audience), click on the blue line at the bottom of the CamDirector preview to drag the audience exclusion line up (2 below) or down to exclude the people that you need to exclude from the tracking system and save the new setting. For instance:

Make sure not to set this too high, it should never be above the waist of the teacher.