GLASS HALF FULL - The bottom half of each magazine causes additional damage.
Glass Half Full gives a scaling damage bonus that increases to a 6% damage bonus at the bottom of the magazine
In Destiny, GLASS HALF FULL is a Weapon Upgrade that can be found on Auto Rifles and Pulse Rifles. Weapons in Destiny pull each Upgrade at random from specific pools (with a few Weapons that are an exception). This upgrade gives more damage the further into the magazine you go (from the bottom half down) up to 6% at the bottom.
To see more info on exactly which Weapons this Upgrade can be found upon click the link below:
Weapon Upgrade Table
To see more about how this Weapon Upgrade fits into these pools, please click the links below:
AUTO RIFLE WEAPON UPGRADES
MACHINE GUN WEAPON UPGRADES
PULSE RIFLE WEAPON UPGRADES