The best description I've read about CBM is from BeachMusicOnline.com - this a repost of their description:
Beach Music – music style made popular in the Carolinas, it combines many styles that may include but are not limited to Rhythm and Blues, Soul Music, and a little bit of Disco. Basically anything you can “Shag” to (The Shag, or Carolina Shag, is a dance style that has been around almost forever. We are not referring to the slang term made popular by a major movie personality portraying a British spy from the 60’s)
When you ask the question”What is Beach Music?”, you will hear a wide variety of answers. Some may try to define the genre, some may simply describe the feeling they get when they hear Beach Music. Ask the person answering the question how they associate themselves with beach music and you may understand their comments. Old School DJs will tell you something different than guys that have only been playing in bands for a few years. Shag Dancers will have different definitions than the fans of the bands. You may hear varied answers depending on which state the person lives in or was born.