There isn't a specific term for a hollow glacier. However, depending on the specific type of hollow and its formation, you might describe it using these terms:

* Crevasse: A deep crack in the surface of a glacier, often formed by movement and tension.

* Moulins: Vertical shafts that form when meltwater falls into a crevasse or other opening in the glacier.

* Glacial cave: A cavity formed within a glacier by melting ice, often caused by geothermal heat or surface water.

* Ice tunnel: A passageway formed within a glacier, often by meltwater flowing through it.

* Glacial sinkhole: A depression on the surface of a glacier formed by melting ice, often collapsing to form a crevasse.

To better understand what kind of hollow you're referring to, please provide more context or details about its location, size, and how it formed.