A landform. (Geography/Geomorphology)
An isolated rocky mass (the name is German for "island-mountain") in a desert environment, the end stage of the erosion of mountains in said environment.
Inselbergs are essentialy mountains overwhelmed by their own debris, as alluvial fans merge along one side of a mountain range into bolsons, which eventually pile up and merge with bolsons from the other side of the mountain range and from neraby mountain ranges into bajadas.
In a moist climate, such a remnant is called a monadnock, sticking its lonely head up out of a peneplain.