When capitalized: An
GUI (graphical user interface) operating system first released in 1986 by Microsoft Corporation.
When not capitalized: A glass plate inside of a wall that lets light into buildings.
Every operating system has errors and crashes every once in a while, no matter if you're running Windows, Macintosh, Linux, or whatever. Deal with it, guys!
"ABC says they were 'Still The One' back in '77, but they NEVER were the one!"