The phrase "glass rectangle" refers to an object or shape that is made of glass and has four straight sides, with each side forming a right angle. It can be something like a window or a smartphone screen. Full definition
The format, made popular by Snapchat and Instagram, is the native genre of glass rectangles. (flipboard.com)
It consists of a dozen identical triptychs — each comprising wood - framed, colored glass rectangles — and three bronze sculptures displayed in vitrines like medieval church relics. (nytimes.com)
With it being just 6.9 mm thin, the phone feels really small in hand, and the aforementioned curves stop it from feeling like a cold glass rectangle block. (9to5google.com)