drain line for the water that is generated during the defrost cycle for the freezer compartment. normally this water will drain down into the refrigerator section right below the freezer inside the fridge at the very back ...there should be like a funnel cup looking piece with a hose attached that takes the water to a drain pan below your refrigerator....check to make sure this drain is not plugges and causing the water to over flow into the fridge. call for professional help when you get frustrated with trying to DIY. good luck LJ