A rock climbing term for a crack in the rock that is the right size for hand jamming (which is to say jamming the crack with your hand).
While there are various cracks all over the world, Indian Creek, Utah is chock full o'cracks, and not just crappy, flaring cracks, but amazing splitter cracks of all sizes out the wazoo! There's also Yosemite, of course. Yosemite has everything, from bouldering to cracks to face climbing to aid climbing.