What is amorphous solids
Peer through a microscope inside some glass and you'll find the molecules from which it's made are arranged in an irregular pattern. That's why glass is sometimes referred to as an amorphous solid (a solid without the regular crystalline structure that something like a metalwould have). You may also see glass described as a "frozen supercooled liquid". This is another way of saying "glass is a liquid that has never set", which is the puzzling statement you'll sometimes find in science books. We could say glass is a bit like a liquid and a bit like a solid. It has an internal structure that is somewhere between the structure of a liquid and a solid, with some of the order of a solid and some of the randomness of a liquid.
Glass is by no means the only amorphous solid. It's possible to make a type of water called amorphous ice that could be described as in-between solid (water) and liquid (ice). You do this by cooling water very quickly. The ice forms so fast that it doesn't have time to build up its normal, crystalline structure. So what you get looks like ice but behaves in some ways like liquid water. Other substances can be made into amorphous solids too. Solar cells are often made from something called amorphous silicon.