Jeff is right - it does mean OTHER. We have certain codes for different rooms - KT, DN, LR, FR, MBR, 2BR, 3BR, 4BR, OT, OT2 - on the listing sheet
OT could be a bonus room, a 5th bedroom, a second kitchen or 2nd family room.. or any other room that doesn't fit the descriptions. We only have space to list 1 kitchen (KT) for example, so if there is a second kitchen in the house, that would be an OT.
Many times if you read the description of the property you can figure out what the OT stands for...