A hogshead is a type of cask used to mature spirits – typically whisky. They are approximately 225-250 litres and after barrels (which are a bit smaller), hogsheads are the second-most common type of cask used in maturing Scotch.
It’s generally thought that the larger size of hogsheads makes them better suited for longer period of maturation compared to standard barrels. This is due to the larger volume being favourable for the economics of dealing with the loss of spirit through evaporation (storage costs vs volume of fluid maturing).