I've kind of shied away from that box because from what I've heard and read, a lot of it is like R&B or jump blues or something like dance music. It developed to replace the swing music that people could dance to whereas isn't the sort of music you could. I'm not sure how to define it, but maybe it's closer to pre-rock, with a lot of honking. This is probably not too helpful but it's the kind of thing that you know when you see it or hear it. I recently listened to one of those Prestige First Sessions, the one with Lockjaw and Bennie Green and it was way disappointing for the most part because it was R&B, with a lot of vocals.
I just looked at AMG and they define it sort of as I described it, as dance music, where the musicians played louder, with more electric instruments and accentuating riffs, boogies and vocals. Pianos pounded harder and louder and ditto for the saxes.
That said, R&B did play an important part in jazz. For example, Sonny Stitt played with Tiny Bradshaw and Coltrane played in a R&B band and this proved an important training ground for jazz musicians.