Define coordination number. How does this differ from atomic packing factor?

Coordination number:

Coordination number can be defined as the number of nearest atoms which touch the central atom. In simple word the number of neighbours atoms which touches a an atoms.

Atomic packing factor:

It is also known as packing efficiency. It is the fraction of volume in a Crystal which is filled by constituent particles. It is always less than 1. Generally it is represented in the fraction.

Ex:

Lets take FCC cubic cell

Coordination number = 12.

Atomic packing factor = 74%