(NEXSTAR) — While some may view Memorial Day as the unofficial start to summer — and the chance at a three-day weekend — the day carries a heavier meaning.

Memorial Day, which falls on the last Monday in May, honors Americans who gave their lives in service. It was declared a national holiday by Congress in 1968.

The day’s history technically started more than 100 years earlier when, in 1866, Waterloo, New York, held a city-wide ‘Decoration Day.’ According to USO, citizens were encouraged to place memorials on the graves of soldiers.

Two years later, Maj. Gen. John A. Logan, the head of the Grand Army of the Republic, an organization of Union veterans, established the first-ever national Decoration Day, a time for the nation to decorate the graves of the war dead with flowers. He moved the day to May 30, a time when flowers would be in bloom.

Until World War I, Decoration Day honored those who fought in the Civil War. In the decades since its inception, the day became better known as Memorial Day, the Department of Veterans Affairs explains. Congress designated Memorial Day as a national holiday through the Uniform Holiday Bill passed in 1968 – it took effect in 1971 – and formally moved it from May 30 to the last Monday of the month.

Memorial Day is often confused with Veterans Day, which falls on November 11 every year and honors those who fought in American wars and were discharged under conditions other than dishonorable. Veterans Day, originally known as Armistice Day, became a legal holiday in May 1938.

After World War II, Armistice Day was renamed Veterans Day as part of the Uniform Holiday Bill.

Memorial Day should also not be confused with another military holiday in May, Armed Forces Day. Celebrated on the third Saturday of the month, Armed Forces Day honors those currently serving in the U.S. military.