Dirt jumping is when people ride bikes and do cool tricks and jumps on specially made dirt tracks. Imagine playing with your toy cars in a sandbox, but instead of cars it’s people on bikes and instead of just driving around you’re jumping and doing tricks on hills made out of dirt.
The dirt tracks usually have a lot of bumps and jumps called "berms" and "tabletops". Riders will pedal fast and hit the jumps at just the right angle to get some air and do tricks like spins and flips before landing back on the track.
Riders wear special helmets and padding to keep them safe in case they fall. It’s a really fun and exciting sport to watch!