What's the difference between a powerlifting bar, an Olympic-lifting bar, and a general-purpose bar?

Powerlifting bars are stiff with aggressive knurling for squat/bench/deadlift; Olympic-lifting (weightlifting) bars use faster-spinning sleeves and more whip for snatch and clean & jerk. Most bars in this pool are 28–28.5 mm general-purpose shafts that r/BarbellMedicine describes as fine for powerlifting, CrossFit and amateur weightlifting but not specialized for serious Olympic lifting.