Jumping both wheels while rolling, with no ramp and no ledge. Not one simultaneous heave but two beats: front wheel up first, then drag the rear one after it.
The bunny hop is the base for almost every street and park trick, and in cyclocross it's the alternative to stepping off at a barrier. The move has two beats: drop into your knees, push the hips back and pull the bar with you until the front wheel snaps up — and the moment it's up, extend your legs, push the bar forward and up and drag your feet after it. The most common mistake is trying to heave both wheels at once, which only produces a hop. Behind that come too little front-wheel pop, working from the arms alone, and looking down. Height comes from timing and explosive leg extension, not from pulling harder. Two things people miss: learn it on flat pedals, because clipless cheats the rear wheel up and hides the technique. And practise over a loose stick or a rope — a kerb blocks the wheel and throws you.