behind the beat.

I like to envision it as fitting with the classic "Mary J. Blige" dance:

https://www.youtube.com/watch?v=CQ9wybq0T1g

And it's not just mid-tempo or jazzy stuff. Any big hit from popular Black music you can think of from the last 60 years that wasn't a slow ballad had this quality. New Jack Swing, Babyface, everything from the 70s, etc. I like to call it the "Pregnant Two/Four" because when you snap your fingers to it, there's a tendency to wait as long as possible before you snap on two and four - you're behind the beat a bit. Contrast this with most Rock, for example. It wouldn't be "wrong" to snap that way in Rock, per se, but Rock music, excluding the stuff that openly tried to sound bluesy, was much straighter. Modern Black popular music is very straight, in this way.

This is the element Bruno Mars tapped into and why all the 24K Magic songs have been so big - he put swing and groove (basically leaning behind the beat) back into the songs and pulled the music away from the heavy, straight, thump-a-dump Trap/Hip-Hop feel. Of course, he also copied alot of artists stylistically, but that's not the point.

Kids today don't have as much exposure to music being rhythmically loose and swingy like that, so that quality is only appreciated by old heads today.