Static friction occurs when two bodies are in contact and are pressed against each other by a force. A simple example is a block resting on the ground, where its weight (gravitational force) equals the normal force pressing it against the surface. To move the block, a force must be applied parallel to the ground. It is observed that the block does not start to move until the applied force reaches a certain threshold. The applied force is initially counteracted by an equal and opposite force, which can be interpreted as static friction.
As soon as a critical force $F_\mathrm{HR}^\mathrm{k}$ is exceeded, the block begins to move. Since, in an idealized model, a body makes contact with the ground at only three points, this critical force is, to a good approximation, independent of the contact surface area and directly proportional to the normal force. The proportionality constant is called the coefficient of static friction $\mu_\mathrm{HR}$, and the following relation holds:
$$
\vec{F}_\mathrm{HR}^\mathrm{k} = \mu_\mathrm{HR} \vec{F}_N
$$
Since the body is not moving and no energy is converted into other forms such as heat, static friction is not a form of friction in the narrow physical sense. Nevertheless, it is still referred to as friction.