Here's the wikipedia definition of Soul Music:

"Soul music is a music genre that combines rhythm and blues and gospel music, originating in the United States. According to the Rock and Roll Hall of Fame, soul is "music that arose out of the black experience in America through the transmutation of gospel and rhythm & blues into a form of funky, secular testifying."

There's more here.

**

My definition of soul music: Soul music is music that speaks to, soothes, and inspires the soul. Soul music may be soley instrumental, or it might include vocals. It's not the tune or words but how they are played and sung. As far as I'm concerned, soul music can secular or religious, but true soul music must be spiritual, in the deepest sense of that word.

In that sense, one facet of soul music for me are many of the examples posted in this Mudcat thread: thread.cfm?threadid=105855 "Religious Songs That Speak To You"

But, that's only one facet of what I consider soul music. Here's an example from the secular category of songs:

http://www.youtube.com/watch?v=cft0cl-j_JE
Isaac Hayes - Walk On By (Live at Music Scene 1969 Bozo)
from Isaac Hayes' Hot Buttered Soul album: