It is not a well researched web page. But the meaning is literal: it means "like glass"
Forminafera are a type of single cell creature, rather like an amoeba, but with a shell. The shells can be made of various different materials.
The shells (called "tests") have a variety of appearances, when viewed under a microscope. Some appear "porcelaneous", they look like fine china, with a shiny white surface. Others have a fine structure that allows light to pass through. The appear like soap bubbles or blown glass. They are not actually made of glass, they are made of a form of calcium carbonate called calcite. These shells are good indicators of sea temperatures, and the white chalk cliffs and limestones are made of trillions of forminafera tests.
Forminafera by J.R Haynes gives details.