Rock crawling is a sport in the rc industry that involves a very slow, low geared rc car with high centre of gravity and loads of torque.
The rock crawler is made to go over obstacles other rc cars wouldn't manage.
Usually rock crawlers are brushless (electric) so they can reach top speeds in a short period of time, they are also well balanced and light so that they can easily go up obstacles.
Some rock crawlers can climb at almost 90 degree angles.
This is due to their outstanding grip and torque.
Most rock crawlers don't go above 1/10th scale as too big of a rock crawler makes the sport too easy and less fun.
Here's an example of a rock crawler in action.