Wind eroded snow, which often looks rough like frozen waves. Usually found on windward slopes.

Wind erodes from the windward side of an obstacle and deposits on the lee side. We call the eroded snow sastrugi. You can recognize it by its rough, sand-blasted texture. We usually think of wind eroded snow as being stable because stress on buried weak layers has been decreased by wind eroding the overlying snow. Conversely, wind will deposit that same snow on to the lee slopes, which increases weight on buried weak layers.

Sastrugi is not always stable snow. Remember you only see the surface texture. Perhaps the wind only eroded an insignificant amount of snow and a buried weak layer still lingers below just waiting for a trigger. As usual, all slopes are guilty until proven innocent by the usual battery of snow stability tests

Additional Terms:
Anchors Hard Slab Avalanche Slide
Aspect High Danger Sluff
Avalanche High Marking Snowpit
Avalanche Path Isothermal Soft Slab Avalanche
Avalanche Transceiver Layer, Snow Stability
Bed Surface Leeward Stability Test
Collapse Loading Starting Zone
Concave Slope Loose Snow Avalanche Stepping Down
Considerable Danger Low Avalanche Hazard Sun Crust
Convex Slope Melt-Freeze Snow Surface Hoar
Cornice Metamorphism, Snow Sympathetic Trigger
Corn Snow Moderate Danger Temperature Gradient
Couloir Persistent Weak Layers Terrain Trap
Cross Loading Point-Release Track
Crown Face Probe Trigger
Danger Ratings Propagation Trigger Point
Deep Slab Avalanche Rain Crust Upside-Down Storm
Density, Snow Remote Trigger Weak Layer
Depth Hoar Rime Weak Interface
Dry Snow Avalanche Runout Zone Wet Snow Avalanche
Extreme Danger Sastrugi Windward
Faceted Snow Settlement Wind Loading
Fracture Ski or Slope Cut Wind Slab
Glide Skinning, Skin Track Whumpf
Graupel Slab