Netting is a nylon fabric in which the warp and weft yarns are looped or knotted to create open spaces in the fabric.
Tulle is essentially a special type of netting with a lower denier, which means the individual fibers are finer. Tulle is lighter than netting, and the spaces between threads are smaller. It is often starched to give it more stiffness, which is why tulle is frequently used to add volume.
Both tulle and netting are great for formal apparel, hats, tutus, decorations, and more.