UrMet is a magic Runeword created by combining a Ur Rune of Ritual and a Met Rune of Invocation.
How to Create UrMet
You can create UrMet by adding the magic Ur Rune of Ritual and the magic Met Rune of Invocation to a two-socketed Helm, Chest Armor, Pants, or Two-Handed Weapon.
Ur - Your Minion or Companion kills an enemy or dies. (10)
Met - You leave the Necromancer's Desecrated Ground behind you for 3 seconds, dealing damage to enemies within. (100)
Overflow
UrMet can not overflow because the amount of Offering you receive from the Ur Rune exactly fills the required Offering of the Met Rune.
Overflow occurs when your Ritual generates more Offering than required for the Invocation. The overflow effect is proportional to the amount Offering overflows.