Aim down sights
From Destinypedia, the Destiny wiki
Aim Down Sights is a gameplay mechanic featured in Destiny and many other First-person shooters. When aimed down sights, or ADS, the camera angle shifts to behind the weapons sights. This generally makes the weapon more accurate, and may provide some zoom. ADS is usually used at longer ranges.
Gallery
The Viper P3 when aiming down sights.
