rugosity

Rugosities are minuscule, ridgelike corrugations on a rock surface—generally having an inch or less of relief—which bring to mind wrinkled skin. Climbers sometimes grip rugosities with their fingertips to ascend vertical terrain, and refer to such features as crimps or crimpers. If a rugosity exists as a discrete bump rather than a tiny elongated ridge, it is called a nubbin.

Jon Krakauer