The gold certificate was used from 1882 to 1933 in the United States as a form of paper currency. Each certificate gave its holder title to its corresponding amount of gold coin. Therefore, this type of paper currency was intended to represent actual gold coinage. In 1933 the practice of redeeming these notes for gold coins was ended by the U.S. government and until 1964 it was actually illegal to possess these notes (in 1964 these restrictions were lifted, primarily to allow collectors to own examples legally, however the issue technically converted to standard 'legal tender' with no connection to gold).
Gold certificates were issued in the pre-modern era of U.S. paper money before 1928. When U.S. paper money was modernized (made smaller, as we know it today, with fewer variations or "types") in 1928, gold certificates ceased to be issued.
When the U.S. was taken off the gold standard in 1933, gold certificates were withdrawn from circulation. As noted above, it was illegal to own them.