Glass is an amorphous (amorphous solid) (non-crystalline (crystal)) solid material. Glasses are typically brittle, and often optically transparent. Glass is commonly used for windows, bottles (Glass Bottles), and eyewear; examples of glassy materials include soda-lime glass, borosilicate glass, acrylic glass, sugar glass, Muscovy-glass (Muscovite), and aluminium oxynitride. The term glass developed in the late Roman Empire. It was in the Roman glassmaking center at Trier, now in modern Germany, that the late-Latin term glesum originated, probably from a Germanic (Germanic languages) word for a transparent (transparent materials), lustrous substance.

Strictly speaking, a glass is defined as an inorganic product of fusion which has been cooled through its glass transition to the solid state without crystallising. Many glasses contain silica as their main component and glass former. The term "glass" is, however, often extended to all amorphous solids (and melts (melt (manufacturing)) that easily form amorphous solids), including plastics, resins, or other silica-free amorphous solids. In addition, besides traditional melting (Glass production#Hot end) techniques, any other means of preparation are considered, such as ion implantation, and the sol-gel method. Commonly, glass science (:Template:Glass science) and physics (physics of glass) deal only with inorganic amorphous solids, while plastics and similar organics are covered by polymer science, biology and further scientific disciplines.

Glass plays an essential role in science and industry. The optical and physical properties (physical property) of glass make it suitable for applications such as flat glass, container glass, optics and optoelectronics material, laboratory equipment, thermal insulator (glass wool), reinforcement fiber (glass-reinforced plastic, glass fiber reinforced concrete), and art (Glass art).