On the Billboard charts dated Oct. 22, four full-length releases that qualify for the Americana/Folk Albums chart -- Bon Iver's 22, A Million, Bob Weir's Blue Mountain, Van Morrison's Keep Me Singing and Drive-By Truckers' American Band -- landed among the top 10 highest-selling albums overall (in the tracking week ending Oct. 6, according to Nielsen Music). That's an outsize performance for Americana, and represents more in sales than any other genre outside of rock (for which all four also qualify) among the top 10. In other words, Americana albums outsold R&B/hip-hop, dance and, most notably, country among the Top Album Sales chart's top 10. It's the first time the genre has bested country sales among weekly top 10-sellers since Billboard rebranded the Folk Albums chart as Americana/Folk Albums beginning with the chart dated June 4.

While that may seem surprising -- particularly given the star power that dominates the Top Country Albums chart, led this week by Jason Aldean, Florida Georgia Line and Chris Stapleton -- it's the latest milestone in a larger trend surrounding the emergence of Americana into the commercial mainstream.

"I think it's burgeoning in the commercial marketplace for a community that already existed in a non-commercial marketplace," says Jed Hilly, executive director of the Americana Music Association. "I think that the fact that there's a word in the dictionary, there's a Grammy Award, [now] there's a place for these artists who don't necessarily fit in the mainstream commercial boxes, but do have artistic similarities can call home."

As Hilly notes, for a term that's been traditionally used as a catchall for traditional American music, Americana has become more accepted as a legitimate musical genre over the past several years. In 2010, for instance, the Grammys awarded the first-ever Best Americana album, which went to Levon Helm for his Electric Dirt LP; categories for Best American Roots Song and Best American Roots Performance were introduced in 2014 and 2015, respectively. In August of 2015, Merriam-Webster officially added the word to its dictionary, defining it as "a genre of American music having roots in early folk and country music."

And in May, Billboard announced the rebranding of the Folk Albums chart following in-depth dialogue with industry contacts, writing the chart would "spotlight the middle ground bridging country and rock: organic, roots and acoustic-based groups and solo singer-songwriters." That laid the groundwork for this week's milestone, which benefited greatly from five new titles debuting in the top five spots on the Americana/Folk Albums chart.

Of course, the inclusion of Bon Iver -- whose 22, A Million leans more electronic than his previous releases -- certainly helped boost Americana's footprint this week, but Hilly doesn't consider genre lines to be concrete. "Americana is a funny genre, because in some ways it can be very inclusive because it spans from blues to gospel to bluegrass influences, and it's a grittier style that crosses genre boundaries in some ways," he says. "I think all genres are expansive; I don't see any point in arguing. I just see it as a bigger conversation in the evolution of musical styles. What is rock today? It's not Chuck Berry and the foundations of rock and roll."

Hilly, though, does have his own turn of phrase when it comes to a straight definition of the word Americana. "Merriam-Webster's is not far off, but today I think it's gone way past that," he says. "If you can taste the dirt through your ears, that's Americana."