XolLum is a legendary Runeword created by combining a Xol Rune of Ritual and a Lum Rune of Invocation.
How to Create XolLum
You can create XolLum by adding the legendary Xol Rune of Ritual and the magic Lum Rune of Invocation to a two-socketed 
Helm, 
Chest Armor, 
Pants, or 
Two-Handed Weapon.
Overflow
When XolLum overflows, you receive the Lum Rune's overflow effect (Increased Resource Restored) 29 times.
Overflow occurs when your Ritual generates more Offering than required for the Invocation. The overflow effect is proportional to the amount Offering overflows.
Legions
Helltide