(WASHINGTON) -- While Memorial Day is the unofficial start of summer, celebrated by many with cookouts and pool parties, the holiday's purpose is one of remembrance for the country's fallen soldiers.
This year, the USAA Poppy Wall of Honor -- a temporary installation honoring the more than 645,000 Americans who, since World War I, have been killed in military service -- has returned to the National Mall in Washington.
The tribute, a lightly reflective display of shocking red petals, is on display between the Vietnam Veterans Memorial and Constitution Gardens pond. It returns to Washington for the first time since 2019 after being on hiatus during the COVID-19 pandemic.
Its name is also special: The poppy flower came to symbolize combat sacrifice after Canadian Lt. Col. John McCrae saw bright red poppies blooming in the battle-torn wake of World War I and was moved to write "In Flanders Fields." McCrae's work was later published and seen by American University of Georgia professor Moïna Michael and by Anna Guérin in France. Micheal wrote her own poem in 1918 titled "We Shall Keep Faith" and began selling poppies to raise money for veterans and their families; she is credited with the idea of making and selling red poppies to help support veterans.
In France, Guérin organized her own large poppy drives and sold the flowers for money for widows, orphans and veterans.
It is with that legacy in mind that the flower wall again blooms in memory of the slain.
"Memorial Day may be our most sacred holiday," Vice Adm. John Bird, senior vice president of military affairs at USAA, told ABC News.
"We take time to remember and reflect on the men and women that died in service to our country fighting for our nation. Many of these young men and women were volunteers," Bird says. "They put their lives on the line so we can enjoy the freedom and the quality of life that we have today. So it's a very important holiday and we can never thank them enough, but we certainly should never forget them."
Military leaders also note that there can be a common misconception about the holiday's meaning compared to Veterans Day, in November.
"A lot of folks don't understand the significance of it … people say, 'Hey, have a great Veterans Day.' The veterans -- they're living. It's a little hard to say, 'Hey, have a great Memorial Day.' We're really honoring those that died during war on Memorial Day and we must keep that in mind," said Air Force Chief Master Sgt. Dennis Fritz.
Though the holiday is rooted in solemnity and sacrifice, it can also be an occasion to gather in celebration for those who cannot, supporters say.
"Reflect on them for a moment and be thankful if you know family members of the fallen. Thank them for their great sacrifice ... It's not to say we don't have a good time or we don't enjoy our barbecue," Bird says. "Just take a moment to thank those who have fallen, wear a poppy and remember and reflect."