What exactly is a VLCC?

Crude oil tankers are classified in different ways according to their deadweight tonnage, structure, etc. Here are some common types:

Classification by Deadweight Tonnage 
Panamax: Deadweight tonnage is generally between 60,000 and 80,000 tons. Specifically designed to transit the Panama Canal, the vessel's dimensions are limited by the size of the Panama Canal locks. Primarily used on regional routes along the US coast, the Black Sea, and the Far East.

Aframax: Deadweight tonnage is typically between 80,000 and 120,000 tons. This is a high-demand vessel type, mainly used on short-haul routes in the North Sea, Black Sea basin, China Sea, Caribbean Sea, and Mediterranean Sea. 
Suezmax: Deadweight tonnage is generally between 120,000 and 200,000 tons. Designed to be able to transit the Suez Canal at full load. Often used to transport crude oil from the Middle East to Europe via the Suez Canal. 
Very Large Crude Carrier (VLCC): Deadweight tonnage is between 200,000 and 320,000 tons, carrying between 1 and 2 million barrels of crude oil. Widely used to transport large quantities of oil from the Gulf, West Africa, North Sea, and Prudhoe Bay to North America, Europe, and East Asia.