TONNAGE and TONNES Explained. ( GT, GRT, NT, NRT, LIGHT WEIGHT and DEAD WEIGHT )

What is Gross Tonnage (GT) ? What is Gross Register Tonnage (GRT)? What is Net Tonnage (NT) ? What is Net Register Tonnage (NRT) ? What is Dead Weight ? What is LIGHT WEIGHT ? What is DISPLACEMENT ? FOR MARINE ENGINEERS.