It's where you combine a bunnyhop with a pedal stroke. 3/4 means that you "kick" the pedal three quarters around. (270 degrees). That kinda kick's you up on the rearwheel and forward, from full or part still-stand. The pedal kick get's you forward and the J-hop get's you up. (J-hop is like a bunny-hop, but from rearwheel position.)
yah dudu, like when I hope on a jay, it like feels like I get cranked a full 270 too...or maybe 420... anyways I sure get high, and then I feel like I wanna get a table top, or a piknik table to sprawl.
I don't know what any of this has to do with bunny hops though, isn't that like a bmx trick or something?
Seriously though, I always get higher on a j-hop. I use a whole lot of compression re-bound in my fork and a 3/4 crank and I get way higher than an average bunny hop by me -- but I suck at bunny-hops: 1 foot max. J-hop: 2' if I'm lucky.
I memorialize the day I learnt how to j-hop properly.