The phrase "40 ounce" typically refers to a single glass bottle of malt liquor, a form of beer noted for its high alcohol content by volume. Depending on their size, other beers served in smaller glass bottles and aluminium cans can be combined to reach a total of 40 ounces.
The most common size of American beer can and bottle is the 12 ounce variety. At this size, three and one-quarter beers are required to match the 40 ounce total. Some beers are also available in a 24 ounce "Tall Boy" size. The 40 ounce was popularized by numerous rappers in the late 1980s and 90s.