Western Swing (not to be confused with West Coast Swing) developed within country music in the 1930s and 1940s and often has an up-tempo dance beat.

It draws it's influences from Dixieland jazz and blues blended with swing and is often characterised by the steel guitar or violin. These electrically amplified stringed instruments, especially the steel guitar, give the music a distinctive sound.
Western swing differs in several ways from big band swing of the same era. The bands, vocals and other instruments follow the fiddle's lead and often include improvisations by soloists or collectively.

See the full article on Wikipedia. Listen to some old and new Western Swing Jivers below.