The Tare weight is the weight of a lorry and trailer or railway wagon when they are empty.When they go over a weighbridge the Tare weight is subtracted from the total weight to give the weight of the contents or load,such as Coal or Steel or other items.
tare 2 (t�r)
n.
1. The weight of a container or wrapper that is deducted from the gross weight to obtain net weight.
2. A deduction from gross weight made to allow for the weight of a container.
3. Chemistry A counterbalance, especially an empty vessel used to counterbalance the weight of a similar container.
tr.v. tared, tar�ing, tares
To determine or indicate the tare of, especially to weigh in order to find out the tare.
The question seems to indicate that you believe 'tare' to be an acronym. As Zen's answer shows, this is not the case.
The origins of the word lie with the Arabic 'tarha', meaning 'what is rejected'. It then came via Latin and French (by which time it meant 'deficiency') to its present day meaning of the weight of a vehicle without fuel or load.