Freeflying is the discipline of flying the body in orientations other than the traditional belly-to-earth: head-down, head-up (sit flying), and the transitions between them.
Faster, and a different skill
Because these positions present less surface area, freefly speeds are substantially higher than belly flying — often 160 to 180 mph and beyond. That changes everything from equipment demands to how deployment is managed.
It is also less stable to learn: belly flying is a naturally stable position, while head-down is not, which is why tunnel time is so widely used for freefly progression.
Equipment and separation
Freefly-friendly rigs have secure flap and handle designs because higher speeds and varied orientations can dislodge poorly secured equipment. Drop zones separate freefly and belly groups on a load because of the speed differential.
These pages explain what things are so the language makes sense. They are not instruction and cannot substitute for it — skydiving is taught in person by rated instructors at a drop zone, and anything involving equipment handling or emergency procedures belongs there rather than on a web page.