Americana Radio Dictionary of Terms.
Record promoter Pete Knapp defines Americana music: "When referring to it as a genre, "Americana" can be best explained as an amalgam of roots music fused by the confluence of the shared and varied traditions that categorically make up the American musical ethos; specifically those sounds that are merged from folk, country, rhythm & blues, rock & roll and other external influential styles."

Americana is popularly referred to, especially in print, as "alt-country" or sometimes "". The genre is also referred to by many other names, including "insurgent country", "no depression", "rockabilly", "cowpunk", "progressive country", "regressive country", "roots rock", "twang core", "new americana", "cowpunk", "y'allternative", and many others. While some of these nomenclatures may seem derogatory or unintelligent, they capture the essence of what the New York Times considers "the coolest music scene today".

The Americana Music Association defines Americana music: Americana is contemporary music that incorporates elements of various American roots music styles, including country, roots-rock, folk, bluegrass, R&B and blues, resulting in a distinctive roots-oriented sound that lives in a world apart from the pure forms of the genres upon which it may draw. While acoustic instruments are often present and vital, Americana also often uses a full electric band.

Wikipedia Entries for Roots-Based Musical Genres:

(More definitions to come.)