The weight of an empty truck or large container, used for calculating the weight of the goods that it carries.And according to Collins dictionary:
1. The weight of the wrapping or container in which goods are packed.It can also be used as a transitive verb to mean to weigh (a package etc.) in order to calculate the amount of tare.
2. A deduction from gross weight to compensate for this.
So let us say that you are going to bake a cake and want to weigh baking powder on a digital weighing machine. The tare function will help you by deducting the weight of the container and arriving at the net weight of the baking powder in it.