http://windows.microsoft.com/en-us/windows/history #T1=era0

Microsoft works on the first version of a new operating system. Interface Manager is the code name and is considered as the final name, but Windows prevails because it best describes the boxes or computing “windows” that are fundamental to the new system. Windows is announced in 1983, but it takes a while to develop. Skeptics call it “vaporware.”

On November 20, 1985, two years after the initial announcement, Microsoft ships Windows 1.0. Now, rather than typing MS‑DOS commands, you just move a mouse to point and click your way through screens, or “windows.” Bill Gates says, “It is unique software designed for the serious PC user.”