16:9 is known as High Definition (HD) and it is the international standard format of HDTV, SD (Standard Definition) TV, and analogue system PALplus.
16:9 ("Sixteen-by-Nine" and "Sixteen-to-Nine") is a widescreen aspect ratio used for films, it has the most common aspect ratio for televisions and computer monitors; almost twice as wide as it is high (1.78:1). It is with a width of 16 units and height of 9. 
16:9 aspect ratio resolutions are 1024×576, 1152×648, 1280×720, 1366×768, 1600×900, 1920×1080, 2560×1440 and 3840×2160.

16:9 is the best aspect ratio for taking photos you intend to display on a widescreen TV or widescreen projector. (Most plasma and LCD televisions have a 16:9 aspect ratio). For example, a 3:2 image can be displayed on a 16:9 television, but black bars appear on the left and right of the image because the original image is not wide enough to fill the entire screen. The same picture taken in 16:9 aspect ratio fills the entire screen without black bars.