Overhead garage doors are connected with rollers via hinges and brackets. The rollers sit in the garage door tracks and move upwards and downwards. This is the way each overhead door moves up and down. The trip rollers make along the vertical and horizontal tracks and back down again ensures the garage door is opened and closed fully. If anything disrupts this trip, the rollers will stop and probably jam. The problem is usually found on the tracks. When they are dented ort bent seriously, there is a chance that the rollers won't jam but come off the tracks.
If the rollers come off the tracks, so will the door! That's what we mean by saying that the garage door is off the track. It might take only one damaged roller or bent track section to lead the door off. In this case, the door will probably sag. It must be fixed right away because the door won't move. It will leave the garage unprotected and will also be a safety hazard.