It is a term mainly used to promote modern progressive country, modern western swing, contemporary folk, roots rock, rockabilly, and other American roots music genres not popular in the mainstream.
Other terms for this include "Alternative Country," "No Depression" (this name came from the title of an Uncle Tupelo album and is also the name of the leading Americana Music magazine), "Insurgent Country," "Cowpunk" (in the 1980s), and other names.
A form of made-up, modern American music which borrows from traditional country, bluegrass, folk and blues which is conceived and played by people who haven't explored those genres of music and really don't care to. This music can often be found next to the Starbucks cash register. Typically, Americana musicians superficially pretend to be traditionalists, adopting traditional clothing (vests and overalls) and hairstyles, but secretly dislike real traditional music.
"I hate bluegrass music, but I just got a banjo! I'm going to start an Americana band!" "Dude, you better get a vest."