Ice screw: A protection device for ice climbing. Looks like a large bolt that can be screwed in hard ice.
Index line: the point at which the direction-of-travel arrow meets the housing on a compass and where the degree reading should be read to establish a bearing.
Insulation: A material used to reduce heat loss. Typical insulative materials found in mountaineering products are down, synthetic wadding, foam and gels (see also Fill).
Internal-Frame Backpack: A backpack designed with its frame inside the pack.