The United States twenty-dollar bill ($20) is a denomination of United States currency. U.S. President Andrew Jackson is currently featured on the front side of the bill, which is why the twenty-dollar bill is often called a "Jackson," while the White House is featured on the reverse side.
The twenty-dollar bill in the past was referred to as a "double-sawbuck" because it is twice the value of a ten-dollar bill, which was nicknamed a "sawbuck" due to the resemblance the Roman numeral for ten (X) bears to the legs of a sawbuck, although this usage had largely fallen out of favor by the 1980s. The twenty dollar gold coin was known as a "double eagle". Rather than a nickname, this nomenclature was specified by an act of Congress.