It’s a matter of debate, but it definitely isn’t a solid.

A more elaborate alternative definition is this: “Glass is a non-equilibrium, non-crystalline condensed state of matter that exhibits a glass transition. The structure of glasses is similar to that of their parent supercooled liquids (SCL), and they spontaneously relax toward the SCL state. Their ultimate fate, in the limit of infinite time, is to crystallize.” […]

“On the other hand, any positive pressure or stress different from zero is sufficient for a glass to flow at any temperature,” he said. “The time it takes to deform depends mainly on temperature and chemical composition. If the temperature to which glass is submitted is close to zero Kelvin [absolute zero], it will take an infinitely long time to deform, but if it is heated, it will at once begin to flow.”