Is Glass a Liquid or Solid?

Liquid

Liquid is right!

May be 'supercooled'.

Glass made from sand silicon dioxide (silica) is an amorphous rather than crystaline substance. They have a property known as the glass transition temperature. Bellow this temp they are hard and brittle above it they soften and can be worked. Glass is made by rapidly cooling the hot silica so that no crystals can be formed. It remains amorphous. Amorphous existing in a non crystaline or disordered form. It is some times refered to as a super cooled liquid.

Not a simple A or B answer here, and not one that everybody agrees upon. I found this great article that describes the molecular arrangement of glass, material properties, types of glass, etc. The bottom line conclusion is that there is no "clear" answer. People still use the term super cooled liquid, but it is considered a misnomer.

Some think given long enough all windows will end up as puddles.

I will go for solid - I measured a 35 year glass pane and could not find any sign of flow. maybe solquid will be closer.