Popcorn's popularity as a cash crop dates back to the late 1800s. The variety with which most people are familiar has large kernels that leave big, hard hulls when popped. Not so with hullless, or rice popcorn.
The popcorn hull is the seed, or kernel that, when heated, "pops" under the pressure of the steam that builds up inside and causes the more tender inner portion of the kernel to expand. The resulting piece of popcorn is an inside out version of the unpopped kernel Because most popcorn kernels are relatively large, so are the remaining hulls -- the brown, crunchy portion of a kernel of popped popcorn that's nestled inside the white, fluffy part.
Hulless popcorn does have a hull -- it must, as the hull is the seed, and without the seed there's nothing to pop -- but the kernels are small so the hulls are smaller, more tender, and less noticeable.
Hulless popcorn manufacturers may develop their own varieties for commercial use, and they make it available in regular and microwavable forms. Japanese hulless popcorn is a variety with longstanding use among home gardeners. According to Local Harvest, Japanese hulless popcorn "produces three to six four-inch ears per plant."