The Badlands is a dry landscape located within Equestria, called such because it hardly ever rains there. Pegasus don't control the weather here as it's off of their flight path.
History[]
Prior to the series, Chrysalis and the Changelings were banished into the Badlands after their defeat within Canterlot.
Season 7[]
Ruby, Steven Universe, Pinkie Pie, Applejack and Lapis Lazuli arrive into the Badlands in order to help Ruby fulfill her dream of being independent, and to be a cowgirl.
Ruby and Steven both become trapped here for a while once they ventured too close to the Changeling Kingdom, only escaping by the end of Season 7.