| Term: | Retreat |
| Definition: | Decrease of the length of a flowline, measured from a fixed point. In practice, when the retreat is of a land-terminating glacier terminus, the fixed point is usually downglacier from the terminus, that is, on the glacier forefield. The quantity reported is most often the amount of retreat rather than the length itself. Advance is the opposite of retreat, that is, advance of the terminus. |
| Term: | Retreat |
| Definition: | A decrease in the length of a glacier compared to a previous point in time. As ice in a glacier is always moving forward, its terminus retreats when more ice is lost at the terminus to melting and/or calving than reaches the terminus. During retreat, ice in a glacier does not move back up the valley. |
| Term: | Retreat |
| Definition: | When a mountain glacier's terminus doesn't extend as far downvalley as it previously did; occurs when ablation surpasses accumulation. |