A program that is written to run under the Microsoft Windows operating system, also called a "Windows app." All 32-bit Windows applications run in the 32-bit and 64-bit versions of Windows. All 64-bit applications require 64-bit Windows, which is the standard on new Windows computers and tablets.
Older 16-bit Windows applications can run in the 32-bit versions of Windows, including Windows 95, 98, XP, Vista, 7, 8 and 10. However, 16-bit applications do not run natively in the 64-bit versions of Windows (see Windows XP Mode