The coefficient of friction \( \mu \) is defined as the ratio of the force of friction \( F_{\text{friction}} \) to the normal force \( N \), which is the force exerted by a surface that is perpendicular to the object resting on it.
The formula for the coefficient of friction is:
\[
\mu = \frac{F_{\text{friction}}}{N}
\]
Where:
- \( F_{\text{friction}} \) is the force of friction acting on the object,
- \( N \) is the normal force acting on the object.
This ratio indicates how much friction is present relative to the normal force.
Thus, the correct answer is:
\[
\boxed{(A) \, \text{Force of friction to the normal force}}
\]