UrLum is a magic Runeword created by combining a Ur Rune of Ritual and a Lum Rune of Invocation.
How to Create UrLum
You can create UrLum by adding the magic Ur Rune of Ritual and the magic Lum Rune of Invocation to a two-socketed 
Helm, 
Chest Armor, 
Pants, or 
Two-Handed Weapon.
Overflow
When UrLum overflows, you receive the Lum Rune's overflow effect (Increased Resource Restored) 1 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