VLCC stands for Very Large Crude Carrier - an oil, chemical or petroleum tanker that is generally between 200,000 and 500,000DWT.
VLCS stands for Very Large Container Ship - a container vessel with the capacity to carry around 8000+ TEU.
VLEC stands for Very Large Ethane Carrier - a class of Gas Carrier vessels designed to transport ethane that generally has a capacity of between 70,000 and 90,000 CBM.
VLGC stands for Very Large Gas Carrier - a class of vessel designed to transport LPG (Liquified Petroleum Gas) that generally has a capacity of between 70,000 and 90,000 CBM.
A Vessel is the term given to a large boat or a ship. Merchant mariners working on container ships and tankers, and others in the maritime industry, will usually use the term Vessel instead of ship.