What are inselbergs?

they are formed by volcanic processes that give rise to a rock resistant to erosion

It's a mass of hard rock that has resisted erosion even though the plateau around it has been destroyed. The Uluru is an example. :)

Australia's most famous inselberg, or monolith, is Uluru, or Ayers Rock, in central Australia.

Ayers Rock is Australia's most famous inselberg, or single, isolated mountain of solid rock.