An avalanche caused by snow losing its strength after becoming damp, moist or saturated with water.
Wet Snow Avalanche:

Most avalanche professionals make a hard distinction between dry snow and wet snow avalanches because they are such different beasts. They are caused by different processes, they fail and fracture differently, they are triggered differently and they move differently down the slope. Really, there is a continuum between wet and dry avalanches and professional workers use the words: dry, damp, moist, wet and saturated to describe the continuum. Wet avalanches cause relatively few avalanche fatalities, consequently, they are studied less and are not as well understood.

  Dry Avalanches Wet Avalanches
What causes them? Caused by putting too much additional stress on the snowpack Caused by decreasing the strength of the snowpack
How do they involve people? Triggered by the victims or someone in the victim’s party in 90 percent of cases Difficult for people to trigger. Most accidents are from natural avalanches
What are the contributing weather factors? Usually loading of wind drifted snow or loading of new snow Usually by rain, prolonged melting by sun or very warm temperatures
How do they flow? Fast (80 mph or so) usually with a dust cloud Slower (10-40 mph) like concrete and usually without a dust cloud

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