Celebrate National Oreo Day.
Oreo Cookies are seen May 13, 2003 in San Francisco, California. GETTY

Oreos are undoubtedly the most beloved cookie in the U.S., which is why millions of people celebrate the crème-filled chocolate cookie Monday during National Oreo Day. The delectable snack has been a favorite among sweet-eaters since the black-and-white cookies first popped up on shelves in Hoboken, New Jersey in 1912. However, the original Oreo isn’t exactly the same as the cookie people have come to know and love today.

Celebrate National Oreo Day and learn a few fun facts about America’s favorite cookie below.

1. Oreos started out as biscuits: Although Oreos look similar to the two chocolate disk-shaped cookies with crème filling customers purchase today, the brand wasn’t initially considered a cookie. When Oreos first went to market, they were called Oreo Biscuits. It wasn’t until 1921 when Nabisco, Oreo’s maker, decided to make the change to Oreo Sandwich. In 1937 the name was changed again to Oreo Crème Sandwich and then later in 1974, Nabisco finally settled for Oreo Chocolate Sandwich Cookie, which is currently still on the packaging.

2. No one knows why they’re called Oreos: The history of how Oreo got its name is pretty fuzzy. Some Nabisco officials have said the name was a play on the French word for gold, “or,” which was also the original color of the packaging. Others say it’s a merger of the “re” in cream and the “o” in chocolate to create o-re-o. There are also some people who believe the cookie was named Oreo because it was a short, easily pronounced and easily remembered word.

3. There was once a lemon meringue flavored Oreo: The zesty cookie actually hit the market at the same time the original chocolate cookie sandwich reached shelves. However, the lemon meringue Oreo wasn’t nearly as popular with customers, and the cookie was discontinued shortly after its launch.

4. A mail boy may have created the Oreo design: Urban legend is that a former mailroom employee at Nabisco, William Turnier, designed the embossed print seen on each Oreo cookie disk. Although Nabisco denies the rumor, Bill Turnier, William’s son, allegedly has an original blueprint of the Oreo design, featuring 12 flowers, 12 dashes and 12 dots, with his father’s signature and the date 7/17/52 written on the back.

5. Oreo isn’t the first Oreo-like cookie: Before Oreo, there was actually another crème-filled cookie on the market called Hydrox, which was created by a company named Sunshine in 1908. Hydrox looked incredibly similar to Oreos, except they were a tad bit crunchier than and not as sweet as Oreos.

6. Oreos actually are the most popular cookie in the world: Not only is Oreo America’s favorite cookie – literally more than 450 billion cookies have been sold since the cookie first hit shelves in the U.S. – it’s a favorite cookie globally. The cookies are sold in 100 countries, and in 2014, Oreos grossed about $2.5 billion in sales.