BacQua is a legendary Runeword created by combining a Bac Rune of Ritual and a Qua Rune of Invocation.
How to Create BacQua
You can create BacQua by adding the legendary Bac Rune of Ritual and the rare Qua Rune of Invocation to a two-socketed Helm, Chest Armor, Pants, or Two-Handed Weapon.
Bac - Travel 5 meters. (50)
Qua - Gain 7% Movement Speed for 5 seconds, up to 35%. (50)
Overflow
BacQua can not overflow because the amount of Offering you receive from the Bac Rune exactly fills the required Offering of the Qua Rune.
Overflow occurs when your Ritual generates more Offering than required for the Invocation. The overflow effect is proportional to the amount Offering overflows.