All platforms. Sets your application window to the full-screen native display resolution, covering the whole screen.
This full-screen mode is also known as 'borderless full screen'. Unity renders your application at the resolution set by a script, or the native display resolution if no resolution is set, and scales your application to fill the window. Unity adds black bars ('letterboxing') to the rendered output to match the display aspect ratio, to prevent content stretching. The operating system's overlay UI, such as input method editor (IME) window, displays on top of the full-screen window.