Define spring constant and write its unit.

(N/A) The spring constant,denoted by $k$,is a measure of the stiffness of a spring. It is defined as the restoring force per unit extension or compression of the spring.
According to Hooke's Law,the restoring force $F$ is given by $F = -kx$,where $x$ is the displacement from the equilibrium position.
Therefore,the spring constant is $k = |F/x|$.
The $SI$ unit of the spring constant is Newtons per meter,denoted as $N/m$.