A hogshead (abbreviated "Hhd", plural "Hhds") is a large cask of liquid (or, less often, of a food commodity). More specifically, it refers to a specified volume, measured in either imperial or US customary measures, primarily applied to alcoholic beverages, such as wine, ale, or cider.
A tobacco hogshead was used in British and American colonial times to transport and store tobacco. It was a very large wooden barrel. A standardized hogshead measured 48 inches (1,219 mm) long and 30 inches (762 mm) in diameter at the head (at least 550 L or 121 imp gal or 145 US gal, depending on the width in the middle). Fully packed with tobacco, it weighed about 1,000 pounds (454 kg).
A wine hogshead contains about 300 L (66 imp gal; 79 US gal).
The Oxford English Dictionary (OED) notes that the hogshead was first standardized by an act of Parliament in 1423, though the standards continued to vary by locality and content. For example, the OED cites an 1897 edition of Whitaker's Almanack, which specified the number of gallons of wine in a hogshead varying by type of wine: claret (presumably) 46 imperial gallons (55 US gal; 209 L), port 57 imperial gallons (68 US gal; 259 L), sherry 54 imperial gallons (65 US gal; 245 L); and Madeira 46 imperial gallons (55 US gal; 209 L). The American Heritage Dictionary claims that a hogshead can consist of anything from (presumably) 62.5 to 140 US gallons (52 to 117 imp gal; 237 to 530 L).
Eventually, a hogshead of wine came to be 63 US gallons (52.5 imp gal; 238.5 L), while a hogshead of beer or ale is 64 gallons (250 L if old beer/ale gallons, 245 L if imperial).