Concrete vibrator
A tool that liquefies fresh concrete briefly so entrapped air escapes and the mix flows around reinforcement. Most commonly an immersion head on a flexible shaft.
What does concrete vibrator mean?
Proper technique means inserting vertically at regular spacing, penetrating slightly into the previous lift, and withdrawing slowly enough that the hole closes. Using a vibrator to move concrete horizontally causes segregation, separating stone from paste. Over-vibration drives entrained air out of the mix and can cause aggregate to settle.
In practice
Dragging concrete sideways with the vibrator instead of placing it where it belongs is the most common misuse on residential wall pours.