The pivot point

Pivot points control how objects rotate and scale, and also represent the exact locations of objects in space. All transformations to an object are relative to the pivot point.

You can change the pivot point of an object or the selected components by pressing Insert or Home and using the pivot point manipulator.

Transformation	Relationship to Pivot
Move	Moves the pivot point (and the object travels along with it).
Scale	Scales object out from or in toward the pivot point.
Rotation	Rotates object around the pivot point.