Death World-Ponies call these wild zones-areas where the weather isn’t managed by Pegasus, plants don’t grow under the supervision of Earth ponies and the entire area makes ponies nervous. These zones shrink as more ponies move in, and the area becomes more tame and stabilized, but quite a bit of Equestria itself is civilized areas floating on seas of wild zones. The Everfree forest being the most infamous (and largest) of the wild zones, with everything trying it’s very best to kill you or at least inconvenience you.
Other planets have the same issue, but in a larger scale-it’s harder to herd the weather, the soil is more resistant to Earth pony supervision, and the local predators try to find out how tasty ponies are to eat. Some worlds are the very classic “death world,” where everything on the planet is trying very actively to kill you. And, usually, they succeed at one point or another.
A trivia note-the Griffin Moot builds its basic training camps on death worlds. If the recruit can survive there, they can survive anywhere else.