Foundation loading defines the ability of the soil to support loads applied to the ground. This equation defines a safety limit for the maximum bearing stress that can be applied to a foundation such that it is safe against instability due to shear failure. This ensures the maximum tolerable settlement is not exceeded.
Ultimate Bearing Capacity, `q_"ULT"`, is the derived maximum pressure which can be supported without failure. The Allowable Bearing Capacity is the Ultimate Bearing Capacity divided by a Factor of Safety.
The Factor of Safety (FoS) is by design a value greater than one. A structure with a FoS of 2 will fail at twice the design load.