Ice climbing

Ice climbing is the recreational activity of climbing ice formations and frozen waterfalls. Depending on the slope and texture of the ice, different equipment and techniques can be employed by the climber. For example, on flat ice, almost any good hiking or mountaineering boot will usually suffice. On short, low angled slopes, one can use an ice axe to chop steps. For longer and steeper slopes or glacier travel, crampons are pretty much mandatory for a safe climb. Most mountaineers would only consider the last scenario, true ice climbing.

Reference

Mountaineering: The Freedom of the Hills