If you put a sheet of paper on a table and place your pen in the middle of it, you can rotate the paper whilst keeping the pen in a fixed position.

In doing this, you are rotating the paper about its centre, defined by the position of the pen.

Rotating from centre diagram

Rotating from centre

Static sheet of paper with no rotation.

A full rotation ( {360}^\circ) of the sheet of paper will result in the paper being back in its original position.

In the example above, the centre of rotation was the centre of the rectangle - but what happens when the centre of rotation is outside the rectangle?

Rotating from a centre outside the shape diagram

Rotating from a centre outside the shape

A rectangle with a point of rotation outside the shape.