An aviator, pulling out of a dive, follows the arc of a circle and is said to have pulled 3g's in pulling out of the dive. Explain what this statement means.

When the aviator pulls out of the dive, and follows the arc of a circle, there must be a centripetal force to account for change in the direction of its velocity vector. Due to the property of inertia, the driver of the aviator tends to be in the same state of motion, and therefore experiences large acceleration of the order of 3g.
Pulling 3g’s out of the dive accounts for the driver’s ability to curve the aviator to such an extent that he could withstand an acceleration of 3g.