The set of points on a glacier separating the upper percolation zone, at higher elevation, from the lower percolation zone or wet-snow zone.
The wet-snow line has no surface expression, but is significant as the upper limit of the region where internal accumulation may happen.

Glossary of glacier mass balance and related terms. Working Group on Mass-balance Terminology and Methods of the International Association of Cryospheric Sciences (IACS)