It means that the ecu detected consecutive negative corrections, and reacted (increasing OAR value). Once you do a few more pulls with only positive corrections added, it will trim back to -1.00 OAR.
Think of OAR like fuel trims. The ECU will constantly monitor the amount of knock that can be added (positive corrections). If the ECU detects consistent knock, it will make a global change to the timing table, and the OAR value will reflect this (it is a direct multiplier). So corrections would be similar to STFT and OAR is like LTFT.