Both crystals and metals form structured atomic bonds as they cool and solidify. These bonds are always arranged the same way. Not so with glasses.
Glasses form the same kind of bonds as they cool and solidify as they have when they are liquid.
For this reason scientists classify glass sometimes as a super-cooled liquid, or as an amorphous solid. And rather than a melting point, it has a point at which it will soften and flow when it is heated enough, or it will thicken and become rigid when it is cooled enough. There are many types of glass. It is also fragile and will scratch easily. This term is both a noun, describing something that was etched, and a verb describing a process.