Limiting coefficient of static friction

Definition

Given two surfaces, the limiting coefficient of static friction between them, denoted ${\mu }_s$ or ${\mu }_l$, is defined as the number such that the static friction between any two bodies with these two surfaces respectively as the surfaces of contact cannot exceed ${\mu }_{s}N$, where $N$ is the normal force between the two bodies.

The notion of limiting coefficient of static friction arises as part of the Coulomb model of friction.