This term refers to blues music (often very lo-fi at the time) running back as early as the 1930s (probably even before then) that has very sexually explicit and/or suggestive ("blue") lyrics. These are all very old blues songs whose practitioners extolled the use of drugs, the pleasure of sex, etc. Many such songs stand up today as early underground (then illegal) music with explicit lyrics (often, if not always, by black artists, some of whom even leaned toward lesbianism, such as Lucille Bogan).
Lucille Bogan's "Shave 'Em Dry" and Bo Carter's "Banana In Your Fruitbasket" are prime examples of the dirty blues.
by CinemateryKyle March 10, 2009