Just a quick note for anyone who may NOT know exactly what we're talkin about here.
Play a C chord. Now add the Bb note on the 3rd string. Sounds bluesy right. It's a C chord with a b7. We call it "C7"
Play the C chord again, and remove your index finger from the 2nd string. Play it. Sounds mellow...jazzy..laid back.
That's a C chord with a Major 7th. Noted in books as "Cmaj7".
I appologize if this is too obvious, but I know sometimes folks get them confused.
Good thread Mbo