What does it mean for confidence of detections to be zero in MOT20\train\MOT20-01\det\det.txt?

[WurmD]

In MOT20\train\MOT20-01\det\det.txt we have instances of confidence 1 (i.e., 429,-1,1510,662,104,218,1,-1,-1,-1) and of confidence zero (i.e., 429,-1,90,960,119,119,0,-1,-1,-1)

What does it mean for confidence of detections to be zero here?

[AbdurahmaanYuusuf]

i think it means the class probability is zero