The difference is in how the glacier moves,
- Dry glaciers: In colder climates, basal melting is minimal or absent, and flow is entirely through ductile flow.
- Wet glaciers: In warmer climates, basal slip can predominate.
In Antarctica, thermal regimes pass through the end members of cold, polythermal and warm (wet-based). This means that under some glaciers in cold environments, such as the Dry Valleys in Antarctica, pressure melting point is not reached and the glacier remains frozen to its bed.
This is because a frozen glacier bed inhibits the rapid-flow mechanisms of sediment deformation, ice deformation and basal sliding.
Between these two end members, polythermal glaciers have beds that are frozen and unfrozen. Many small glaciers in Svalbard are polythermal; cold temperatures mean that higher basal pressures must be reached to attain pressure melting point, and thin valley glaciers are typically frozen around their margins but wet-based in their upper reaches[20-22]
Glacial thermal regime
The confusion in that question was because the author of one of the books referred to the glacier below the firn line,
A line across the glacier, from edge to edge, that marks the transition between exposed glacier ice (below) and the snow-covered surface of a glacier (right).
as being dry, which does not describe the glacier itself but how the snow would cover it.