Fitted diapers are just the absorbent part of the diaper, and require a cover to be waterproof. They are cut to the shape of your baby, with elastic at the back waist and legs, thus allowing you to get a good fit with minimal amount of work. You only change the fitted, and not necessarily the cover, at each diaper change.
Pros: more economic, trim, natural fibers, great nighttime diaper if your baby is primarily a side or front sleeper.
Cons: requires separate cover, may require fasteners to hold in place
