BacTec is a legendary Runeword created by combining a Bac Rune of Ritual and a Tec Rune of Invocation.
How to Create BacTec
You can create BacTec by adding the legendary Bac Rune of Ritual and the magic Tec Rune of Invocation to a two-socketed Helm, Chest Armor, Pants, or Two-Handed Weapon.
Bac - Travel 5 meters. (50)
Tec - Invoke the Barbarian's Earthquake, dealing damage to enemies within. (100)
Overflow
BacTec can not overflow because the amount of Offering you receive from the Bac Rune exactly fills the required Offering of the Tec Rune.
Overflow occurs when your Ritual generates more Offering than required for the Invocation. The overflow effect is proportional to the amount Offering overflows.