It’s like half curve/half fastball. Its break is less than a curve, the deepest part is right up by the plate idealy, like you said. I think most people consider it a type of breaking ball, but it usually is a heck of a lot faster than the standard curve.
Freegards
Re your post 49, I thank you for a clear description of the slider. Now I understand.
In my 40s I once had the experience of batting against an aging former major league pitcher (if the OP’s memory was worth a damn I could give you the name...but alas). He threw me an assortment of stuff (probably included the slider) and I trudged back to the dugout.