"Tare" or "tare weight" is the weight of an empty container. Tare is not included in a goods' net weight. So, for instance, 32-oz jar of mayo on the supermarket shelf should actually weight more than two pounds.

A group of 4th graders in Arizona learned this as part of National Weights and Measures Week (save the date: March 5-9), and now you do too. — BEN POPKEN

ADWM Alert June 2007 (PDF) [Arizona Department of Weights & Measures]
Tare Weight [Wikipedia]