What is a bow window? 

bow window or compass window is a curved bay windowBow windowsare designed to create space by projecting beyond the exterior wall of a building, and to provide a wider view of the garden or street outside and typically combine four or more casement windows, which join together to form an arch. SOURCE

Source: www.windowsforyourhome.com

Bow windows are designed to create space by projecting beyond the exterior wall of a building, and to provide a wider view of the garden or street outside, and typically combine four or more casement windows. source