It can be socketed into Weapons and Shields. It can only be inserted into Strength or Meta rune slots.
Aelstrix is one of the Runes available in Lords of the Fallen (LotF). Aelstrix increases the damage of ranged and throwable weapons. For shields, it increases the ammo capacity of said weapons.
The Blackfeather Rangers were renowned for their incredible accuracy with bows, and while few ever competed in Mournstead archery contests, those who did often emerged victorious.
Lords of the Fallen Items