BB rise is the height of the BB axle relative to the axles.
Some say a high bottom bracket makes a bike easier to do gaps and similar moves with.
Some say a lower bb makes a bike more stable for bunnyhops and manuals
Yet others claim that a higher bb is actually better for spinning moves, demonstrated by bmxs having slight bb rise instead of sink.
All I know is, on my Because I can still bunnyhop the same height, but it does feel easier to gap and stuff. FEEL is the key word, I've not actually got any better at it