Fifth (unit)

a unit of measure in spirits (alcohol)

A fifth is a unit of volume which was used for beverages, in the United States. It was called fifth, because it was the fifth part of a US liquid gallon. This means, that it held 25+35 U.S. fluid ounces (757 milliliters). In Europe, it was soon replaced by a bottle size of 750ml, which is one of the common sizes for bottles of wine, sparkling wines, but also of many liquors. The size of 750ml is sometimes called metric fifth, because it uses the metric system.

A metric fifth of Dewar's Scotch whisky