If a liquid is cool rapidly enough it can miss the freezing point and end up as a supercooled liquid.
While all glasses are amorphous solids, not all amorphous solids are glasses; glasses exhibit an actual glass transition. Even though we say solid, a glass is actually a very viscous liquid that moves very slowly over time.
Unlike the crystal an amorphous solid or glass is a disorder arrangement of the atoms of the condensed phase.
At some temperature a supercooled liquid transitions to a more solid or condensed form; this is the glass transition temperature.
The glass in a window (for example) is really a very viscous liquid that moves very slowly over time.
